The Champions League season takes shape Thursday when UEFA draws 32 elite teams into groups in Monaco.
The most coveted prize in club football promises the world's best players performing at arguably their highest level.
Barcelona and Lionel Messi start as favorites to become the first team to retain the title since the old European Cup was rebranded as the Champions League in 1992.
Real Madrid hope Cristiano Ronaldo can help the club to a record-extending 11th title.
Manchester United can end its one-year absence by advancing past Bruges in the playoff round later Wednesday.
With the final five places yet to be decided, here are some things to know about the 2015-16 Champions League group-stage draw:
Bayern Munich vs. Real Madrid to kick it off on Sept. 15? Or Barcelona vs. Arsenal?
It could happen because UEFA scrapped the seeding system which meant the top eight teams ranked by past Champions League performance avoided each other.
Top-seeded status now goes to the title holder and national champions of top-ranked leagues.
That has dropped Madrid and Arsenal - and Man United, if it advances - into Pot 2. Madrid cannot be in Barcelona's group because teams from the same country are kept apart until the quarterfinals.
The new elite includes Paris Saint-Germain, Zenit St. Petersburg and PSV Eindhoven, which would have been in Pot 3 under the old system.
Pot 1: Barcelona, Bayern Munich, Chelsea, Benfica, Juventus, Paris Saint-Germain, Zenit St. Petersburg, PSV Eindhoven.
Pot 2: Real Madrid, Atletico Madrid, Arsenal, Porto, Valencia, Manchester City, (plus 2 from Manchester United, Bayer Leverkusen, Shakhtar Donetsk, Sevilla).
Pot 3: Lyon, Dynamo Kiev, Olympiakos, Galatasaray, Roma (plus 3 from Shakhtar Donetsk, Sevilla, Sporting Lisbon, CSKA Moscow, Lazio, Bruges, APOEL, BATE).
Pot 4: Borussia Moenchengladbach, Wolfsburg, Dinamo Zagreb, Maccabi Tel Aviv, Gent, Malmo (plus 2 from APOEL, BATE, Partizan, Astana).
Only one newcomer to the Champions League groups or European Cup is sure to be in the draw.
Belgian champion Gent won its first national title in May to earn a direct place in the groups.
The Buffalos will be the second-lowest ranked team by UEFA. Only Malmo has a lower UEFA ranking despite reaching the groups for a second straight season.
Astana can debut as the first team from Kazakhstan in the group stage if it gets past APOEL in the playoffs later Wednesday.
Though Borussia Moenchengladbach makes its first group-stage appearance, it was beaten finalist in the 1977 European Cup.
PRIZE MONEY RAISE
The Champions League is not as lucrative as the English Premier League, but is doing just fine.
Booming broadcast rights deals let UEFA increase prize money by 33 percent for each of the next three seasons.
The 32 clubs will share more than 1.2 billion euros ($1.37 billion) in entry payments, results bonuses and shares of television money.
Each gets a basic 12 million euros ($13.1 million), and can earn 1.5 million euros ($1.71 million) for each win and 500,000 euros ($570,000) for draws. Prize money escalates in the knockout rounds.
The biggest earner of UEFA prize money this season should get around 80 million euros ($91.4 million), compared to 60 million euros ($68.5 million) during the previous three-year commercial cycle.
Each goal scored by rivals Lionel Messi and Cristiano Ronaldo will fuel a particular duel.
Both have 77 Champions League goals, tied for the record in the 60-year history of the competition formerly known as the European Cup.
The Barcelona and Real Madrid stars also compete during Thursday's draw for the title of UEFA Best Player in Europe for last season. Messi's Barcelona teammate Luis Suarez completes the shortlist of candidates voted by journalists from each of UEFA's 54 member nations.
Jose Mourinho and Pep Guardiola resume their pursuit of a third European title, trying to equal the record of Bob Paisley (Liverpool, 1977, 1978, 1981) and Carlo Ancelotti (AC Milan 2003, 2007; Real Madrid 2014).
Chelsea's Mourinho would be the first to win with three different clubs. He coached Porto (2004) and Inter Milan (2010) to the title.
RUSSIA vs. UKRAINE
For a second season, UEFA keeps teams from Russia and Ukraine apart.
UEFA made the ruling in July 2014 to avoid fueling tension between the countries during conflict in eastern Ukraine between government forces and pro-Russian separatists.
Russian champion Zenit St. Petersburg is top-seeded and needs to be separated from Shakhtar Donetsk and Dynamo Kiev. Shakhtar has played home games in Lviv while its home city is a focus of fighting.
CSKA Moscow can advance from the playoff round on Wednesday against Sporting Lisbon.
Greek champion Olympiakos is in the draw despite its president, Vangelis Marinakis, being implicated in a criminal investigation of alleged match-fixing.
UEFA rules bar teams proven to have been involved in fixing a match since 2007.
However, the Court of Arbitration for Sport this week dismissed an appeal by Panathinaikos, after UEFA said it had no conclusive evidence from Greece to deny Olympiakos its place.
In 2011, Fenerbahce was withdrawn by Turkey's football federation ahead of the draw, and later served a two-year UEFA ban for match-fixing.
UEFA can also disqualify teams midseason if fixing allegations are proven.
The six-round group stage program kicks off Sept 15 and ends Dec. 9. The top two in each group advance to the two-legged knockout rounds which start Feb. 16.
UEFA picked San Siro in Milan to host the May 28 final but there is no home advantage to play for the famed big-eared trophy.
Neither Milan club - AC or Inter, which have a combined 10 European Cup or Champions League titles - qualified for the second straight season.
San Siro will stage its fourth final, and first since Bayern beat Valencia in a penalty shootout after a 1-1 draw in 2001.
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