Status: 2nd in Premier League
Nickname: The Blues
THE RECORD: The capture of the Champions League trophy has become an obsession for Roman Abramovich since he bought Chelsea in 2005. The Russian oligarch has used his vast resources to transform the club into a European giant, yet the holy grail has continued to slip through his fingers.
A host of semi-final appearances in this competition and their infamous near miss in the 2008 final against Manchester United, when captain John Terry struck the post with a penalty that would have given Chelsea the crown, means the battle to snare the one piece of silver that has eluded the Blues in the last decade continues.
TACTICIAN: Andre Villas-Boas
A Europa League winner with FC Porto last season, the youthful Villas-Boas went back on his own commitment to the Portuguese club when he accepted the offer to take over at Chelsea during the summer.
Just 33 when he accepted a post that has got the better of many more experienced coaches in recent years, his arrival at Chelsea was a homecoming of sorts after his stint as one of Jose Mourinho's backroom staff during the Real Madrid manager's time at Chelsea. Villas-Boas may need to succeed in the Champions League if he is to enjoy a lengthy stay at the helm of the Stamford Bridge ship.
THE GAMEPLAN: Carlo Ancelotti's Chelsea lost their way last season as a lack of width allowed opponents to stifle their attacking intent with too much ease. With an ageing side, the dynamism required to crack open Premier League defences was lacking, while their Champions League challenge ended tamely at the hands of Manchester United in the quarter-finals.
Villas-Boas has vowed to give Chelsea a fresh dimension and that it is much needed as there is a danger this side is growing old and stale together. He may prefer a 4-3-3 formation featuring one striker, but there will always be two of Torres, Anelka and Drogba left unhappy if there is only one central striking position up for grabs.
MAIN MAN: Fernando Torres
If Torres fails to rediscover his best form and emerge as the star turn in this Chelsea side, his presence will become a major stumbling block for Villas-Boas.
The Spaniard, who was once hailed as the finest marksman in world football, has been a shadow of his former self in the last 18 months, with his form after his £50 million move from Liverpool to Chelsea last January alarmingly poor. Villas-Boas may feel under pressure to pick the club's record signing, but he has to be strong enough to jettison Torres if he fails to deliver.
BIG SIGNING: Juan Mata
After failing in numerous bids to sign Tottenham's Luka Modric, Chelsea settled for the capture of the dynamic Mata and the Spain wide man has the class to make a huge impact after his £23.5 million move.
"The main reason I came to this club was I liked the ideas of the new manager here," states Mata. "The first thing Villas-Boas said to me was that he wanted Chelsea to play more attacking football this season and this appealed to me. It means a player of my style can be important to him."
THE RISING STAR: Oriol Romeu
Chelsea prised this talented teenager out of Barcelona during the summer, yet the reigning European champions have not have given up on this product of their celebrated La Masia academy, with a buy-back clause agreed with Chelsea should Romeu become a major star.
He needs to oust experienced operators Frank Lampard, Jon Obi-Mikel, Michael Essien, new signing Raul Meireles and youngster Josh McEacheran to get into a Blues' central midfield line-up and if he's good enough to usurp that quintet, Romeu's value will soar by the end of this season.
THE X FACTOR: The Old Guard
Even during Chelsea's Premier League and FA Cup double-winning season of 2009-10, there was a feeling that the Blues' standard bearers were starting to lose some of their sparkle, with skipper John Terry, midfield stalwart Frank Lampard and strikers Didier Drogba and Nicolas Anelka sliding towards the ranks of veterans.
Two years on and Villas-Boas has to get the best out of these highly-paid, influential characters whose best days are behind them. If he doesn't get the key figures in his dressing room on side, his stay as Chelsea boss could be brief. Alternatively, their support could help him to succeed at Stamford Bridge.
FLAW IN THE MAKE-UP: There are far too many question marks hovering over Villas-Boas and the squad he has inherited to predict just how this season will turn out for Chelsea, though few would place too much money on a side that fell short on all fronts last season coming up trumps with a similar set of players.
Alex and David Luiz are defenders with plenty to prove after coming under fire in 2011, while Lampard, Mikel and Florent Malouda need to confirm they are ready to improve on their efforts of last season. The star-studded front trio of Torres, Drogba and Anelka need to bounce back into top form if they are to save their Chelsea careers.
WHAT THEY SAY: "People say the Champions League is an obsession for this club and you can see why after Chelsea came close so often in the last few seasons, but I will not tell my players to think only about this competition," states youthful boss Villas-Boas. "A winning team targets every trophy and that is my message at Chelsea."
VERDICT: A quarter-final spot should be attainable for Chelsea, but don't expect too much more.
Status: 3rd in Spanish league
Nickname: Los Che
THE RECORD: Champions League runners-up in 2000 and 2001, Valencia have been fighting financial fires over the last couple of seasons and did well to secure direct qualification to the group stage of this year's competition despite the sales of star duo David Villa and David Silva last summer.
A disappointing exit in the first knockout phase of last term's Champions League at the hands of German side FC Schalke was a low point of an otherwise promising campaign for Valencia and they can hope to do better this time.
TACTICIAN: Unai Emery
Emery won praise aplenty for his success in moulding together a fluid and attractive Valencia side even though he was handicapped by the sale of star men, and his tactical acumen was hailed as the key to their success by most pundits.
The exit of star turn Juan Mata means Emery will need to use all his inventive skills to guide his side through to the latter stages of this season's Champions League. This no-nonsense tactical maestro is good enough to do just that.
THE GAMEPLAN: Emery's reading of a game is always impressive and he's not afraid to change his tactics at a moment's notice. Often starting with a lone striker and urging his attacking stars to burst forward in support, he switches to a line-up featuring two out-and-out strikers against lesser sides.
Urging his side to play a pressuring game and favouring the use of dynamic wingers, he will be hoping the loss of Mata is compensated by new signings Pablo Piatti and Dani Parejo, while the dangerous Pablo Hernandez is another important cog in his attacking plan.
MAIN MAN: Roberto Soldado
Soldado had huge shoes to fill as he was charged with plugging the void left by David Villa's exit to Barcelona last summer, yet this cool finisher made his mark as he bagged goals aplenty in his first season at the Mestalla.
He built up a good understanding with Mata last season and will now need to step up to the mark once again as he looks to continue his scoring exploits in the absence of the creative talent who has made the move to Chelsea. His four-goal haul against former club Getafe last April was the highlight of his first season at Valencia.
BIG SIGNING: Pablo Piatti
Mata's exit made the arrival of Piatti even more significant for Valencia coach Unai Emery, with the Valencia new-boy likely to play a key role in the side as either a lead striker on one of the wing raiders.
"I have gone from the desperation of relegation with Almeria last season to the Champions League with Valencia and this is the beauty of football," Argentina international Piatti says. "I'm working for a top coach at this club and could never have dreamed that a move like this would happen when I first came to Spain in 2008."
RISING STAR: Dani Parejo
This gifted midfielder is living proof that a failure to make the step up from the Real Madrid youth team ranks to their star-studded first-team does not necessarily mean an end to dreams of a Champions League career, with his star rising away from the Spanish capital.
His impressive displays as Getafe qualified for the Europa League last season sparked speculation that he would secure a move to a bigger club and Valencia fitted the bill. Champions League success will confirm he is ready for full international honours with Spain.
THE X FACTOR: Sergio Canales
The capture of the Real Madrid starlet on a season-long loan could be one of the best pieces of transfer business this summer, as the 20-year-old has long been tipped to make his mark at the highest level.
His first season in Jose Mourinho's squad did not reap the rewards either player or club would have wanted, so a move to Valencia was a suitable option for all parties. Canales' exciting brand of offensive midfield play should fit neatly into the progressive set-up encouraged by Emery.
FLAW IN THE MAKE-UP: Time will tell whether Mata was the heartbeat of the Valencia revival last season and there must be concerns that his exit will leave an gaping void in a team that has done well to absorb the consistent departures of star men in recent years.
They also appeared to be prone to the odd inexplicably poor performance last season, with their Champions League exit against Schalke and Copa del Rey defeat against Villarreal suggesting they are not ideally suited to knockout football. Their lack of genuine world-class performers means Europe's finest are likely to have too much firepower for them.
WHAT THEY SAY: "I agreed a contract extension at Valencia because I believe in the team we are building," Emery says, having signed a one-year extension to his deal during the summer. "The problem may be that expectation has grown after what we achieved last season, but this is a pressure we should embrace.
"All we want to do is create a team that brings joy to the Valencia fans and playing in the Champions League gives us the perfect chance to do just that."
VERDICT: Valencia should make it through the group stages, but don't expect much more than that.
Status: 2nd in Bundesliga
Nickname: Werkself (Factory Eleven - Leverkusen are the team of the Bayer pharmaceutical company)
THE RECORD: Out of six appearances in the Champions League, Leverkusen's stand-out campaign came in the 2001-02 season when they beat Lyon, Barcelona, Juventus, Liverpool and Manchester United en route to the final before losing to a Zinedine Zidane-inspired Real Madrid in the Glasgow final.
Leverkusen were UEFA Cup champions in 1988, defeating Espanyol on penalties in the final.
TACTICIAN: Robin Dutt
This 46-year-old Cologne-born son of an Indian father and a German mother, Dutt was Leverkusen's first choice to step into the breach after Jupp Heynckes left the club this summer to return to Bayern Munich. He has no top-flight playing experience, only ever turning out in the regional leagues.
Top of his class when he graduated from Germany's national coaching academy in 2005, Dutt cut his teeth at Stuttgarter Kickers but really came to the fore during a four-season spell at Freiburg from 2007 to 2011, transforming the Black Forest side from second division makeweights into a highly-competitive Bundesliga outfit. He is known for excellence at game analysis and strategy and his ability as a communicator.
THE GAMEPLAN: Leverkusen have a long tradition for producing free-flowing and attacking football, flooding forward and taking risks. As an advocate of an enterprising style of play himself, Dutt will seek to stick to the party line in this part of the Rhineland. That said, there is a pragmatic streak in the new coach's mentality and his Bayer are likely to be a shade less gung-ho in their approach.
In their 4-2-3-1 system, the pair of holding midfielders - two from Michael Ballack, Simon Rolfes and Lars Bender - occupy a fundamental role, holding the fort while so many of their colleagues scurry into enemy territory. The left-footed Brazilian playmaker Renato Augusto is the side's brain trust.
MAIN MAN: Michael Ballack
After missing the World Cup in South Africa with a serious ankle injury and sitting out a large chunk of last season with a variety of other physical complaints, there are many observers of the German game who consider the midfield ace to be on borrowed time. However, the former Kaiserslautern, Bayern Munich and Chelsea star is nothing if not intensely proud and will be desperate to make a success of his second stint in Leverkusen.
Germany coach Joachim Low told Ballack that his services were no longer required at international level during the summer and it is fair to say he did not accept the decision with good grace. He may have 98 full caps to ease the pain, 54 of them as captain, but he will be keen to prove his doubters wrong in this season's Champions League.
BIG SIGNING: Andre Schurrle
This fast-rising attacking starlet arrived from Mainz this summer in an €8 million deal. The transfer was signed and sealed a year ago, only for Leverkusen to agree to him staying on at Mainz for one more glorious campaign that saw him fire 15 Bundesliga goals.
Schurrle made his full Germany bow last term against Sweden and scored his first international goal in May in a friendly with Uruguay.
RISING STAR: Sidney Sam
A German of Nigerian descent, this diminutive right-winger or striker can cause mayhem in the toughest of back-lines with his speed off the mark and sheer audacity. He came up through the Hamburg youth ranks and spent a spell on loan to Kaiserslautern prior to signing for Leverkusen at the start of last season.
Capped by Germany at Under-19, Under-20 and Under-21 level, he packs a thumping shot from distance and strikes the sweetest of volleys.
THE X FACTOR: Stefan Kiessling
A long-striding and ever-busy frontman with more than a hint of Jurgen Klinsmann in his playing style, this former Nurnberg man is equally comfortable in the guise of penalty box poacher or willing runner into the channels.
A member of the Germany squad that finished third at the last World Cup, he once earned himself derision aplenty for leaving his boots in the team hotel before an Under-21 game.
FLAW IN THE MAKE-UP: Veteran centre-back Sami Hyypia recently retired and, at first glance, the resultant void has not been filled. Twin central defenders Stefan Reinartz and Omer Toprak lack international experience and, after undergoing an operation on his damaged right-knee, first-choice 'keeper Rene Adler will be out until the New Year.
There also has to be a question mark against the strength in depth of the squad, especially after the departure of midfield dynamo Arturo Vidal to Juventus during the summer.
WHAT THEY SAY: "Leverkusen's strength is their attacking speed and clever movement," former Leverkusen and Germany striker Oliver Neuville says. "In midfield and up front, I'm convinced they have the players to cause Chelsea and Valencia problems in this opening Champions League group. The problem is the departure of Hyypia at the back, as his knowhow and leadership will be badly missed."
VERDICT: The Rhinelanders will be overjoyed to make the knockout stages, but a near-miss is a more likely scenario.
Status: Belgian League champions
THE RECORD: Their only previous taste of Europe's top club competition came in the 2002-03 season, finishing bottom of a first phase group containing Real Madrid, Roma and AEK Athens.
In a decidedly below-par campaign, Genk did not win any of their six games, managing just two goals and failing to make the most of their opportunity against Europe's finest. Their two encounters with Real saw the best and worst of them: a hard-fought 1-1 draw at home and a 6-0 mauling at the Bernabeu.
TACTICIAN: Mario Been
Former Feyenoord, Excelsior Rotterdam and NEC Nijmegen boss Been was recently headhunted to fill the gap left by the shock departure of Frankie Vercauteren for UAE outfit Al-Jazira. He began in management as an assistant to Bert van Marwijk at Feyenoord and was on the coaching staff of Trinidad and Tobago at the 2006 World Cup finals.
Nicknamed 'Mariodona' during his playing days, this Dutch one-cap wonder was a maverick ball-playing midfielder for Feyenoord, Heerenveen and Roda in his homeland as well as Serie A outfit Pisa and FC Tirol Innsbruck in Austria. Been had a reputation for being a dressing room prankster in his playing days.
THE GAMEPLAN: Despite the eccentricities he displayed as a player, Been is much more of a bread-and-butter coach, a convert to the virtues of hard work, discipline, desire and team togetherness. He wants his team to be dominant and proactive and aims to have Genk as well-organised and tenacious as they were under Vercauteren last season.
The left flank of their 4-4-2 is a particularly effective avenue of attack, with overlapping Czechoslovakia full-back Daniel Pudil and boy wonder winger Kevin De Bruyne in tandem. Club captain and defensive midfielder David Hubert holds it all together.
MAIN MAN: Jelle Vossen
Genk fans must have been mightily relieved to discover that their force of nature target man had not, as predicted, left in the summer transfer window for FC Porto. Genk's top scorer last term with 20 goals, he offers tremendous aerial ability, excellent hold-up play and a huge appetite for closing down opponents.
On loan to Cercle Brugge for the 2009-10 season, the 22-year-old is a full Belgium international, winning his first cap in May 2009 in a Kirin Cup match against Chile. His father, Rudi, was a professional footballer, playing in defence for Charleroi and Genk.
BIG SIGNING: Grzegorz Sandomierski
With brilliant young keeper Thibaut Courtois exiting stage left this summer for Chelsea - who promptly loaned him to Atletico Madrid - Genk had to make alternative arrangements and moved to replace him with the towering 21-year-old Pole, who signed on the dotted line from Jagiellonia Bialystok.
A Polish Cup winner in 2010 with Jagiellonia, he has three full caps for his country and some believe he is just as promising as compatriot Wojciech Szczesny at Arsenal.
RISING STAR: Kevin De Bruyne
One of the most talented players of Belgium's new wave, this 20-year-old's silky technique, imagination and elusive running with the ball played a pivotal part in Genk's unexpected march to the Belgian title last term. Signed from Gent in 2005, he made his senior debut for Belgium last season and recently confirmed Chelsea had been in talks over a transfer.
THE X FACTOR: Elyaniv Barda
An effervescent and nimble Israeli winger or striker who comes with a guarantee of crafty assists and smart finishing. Now embarking on his fifth season in Genk colours, he enjoyed an outstanding 2010-11 campaign, scoring 14 and creating another nine goals for his team-mates.
He made his debut for Israel in a Euro 2008 qualifier versus England and has been a regular in the side ever since. Barda played in his homeland for Hapoel Be'er Sheva, Maccabi Haifa and Hapoel Tel Aviv.
FLAW IN THE MAKE-UP: Keeper Courtois saved their bacon so many times last season with timely interventions that they are bound to miss him. They were recently dealt a huge blow when much underrated German centre-back Torben Joneleit was ruled out for seven months with a cruciate knee injury. The sale of striker Marvin Ogunjimi to Mallorca has not helped the cause either.
Franky Vercauteren's departure has left them in the lurch. Mario Been was only appointed in late August and faces a race against time to settle in, draw some quick conclusions and ensure that everybody is pulling in the same direction.
WHAT THEY SAY: "One minute Genk win the league and the next some of their best players like Courtois and Ogunjimi are snapped up by other clubs," ex-Genk midfielder Josip Skoko says. "It always happens at this club and it's so frustrating.
"On paper, the team looks weaker than last season, but they have a strong mentality and surprised many by keeping their heads in the title run-in last season. It's all about doing themselves justice in the Champions League and, while they are in a really tough group, they can spring a shock or two, especially at home."
VERDICT: Enthusiasm aplenty but not nearly enough top-end experience to avoid last-place in their group.