Big-spending Paris Saint-Germain, five-time champion Barcelona and Jose Mourinho's Manchester United are among the teams looking to book a Champions League last-16 place on Tuesday.
The pick of the action sees Anderlecht take on Neymar and Co. in Paris, while Barcelona faces Olympiakos and Roma go head-to-head with Chelsea in Italy.
Here AFP Sport takes a look at what is at stake in each group:
Manchester United vs Benfica: Jose Mourinho's side can secure a place in the last 16 with two matches to spare with a win at Old Trafford, if Basel avoid defeat against CSKA Moscow. United is unbeaten at home in 12 meetings with Portuguese opponents -- its last home loss in Europe came in a 2-1 reverse against Real Madrid in the 2012/13 competition. Benfica is likely heading towards an early exit after losing its first three group games and will be without veteran defender Luisao following his dismissal in the 1-0 defeat by United in Lisbon . Brazilian striker Jonas scored his league-leading 12th goal in a 1-0 win over Feirense on Friday, while United bounced back from a shock loss at Huddersfield Town by edging Tottenham Hotspur 1-0 on Saturday courtesy of Anthony Martial's late winner.
Basel vs CSKA Moscow: Basel will clinch a spot in the knockout phase with a second straight win over CSKA Moscow, if Benfica fail to beat United. After a slow start to the season, Basel has hit its stride with six wins in its last eight games. Conversely, CSKA is in the middle of a terrible run of form after only winning once in its last eight matches and scoring just twice in that period. A 1-0 defeat at Arsenal Tula on Friday left it four points off leader Lokomotiv in Russia, but Alan Dzagoev could return after a month out with an Achilles injury.
Celtic vs Bayern Munich: Celtic matched its century-old British record by stretching its domestic unbeaten streak to 62 matches with Saturday's 1-1 draw against Kilmarnock. But Brendan Rodgers' team faces a stiff test against Bayern Munich as it bids to keep its European adventure alive. A resurgent Bayern eased to a 3-0 win over the Scottish champion a fortnight ago, and a repeat success would all but end Celtic's chances of reaching the knockout rounds. Jupp Heynckes is hopeful striker Robert Lewandowski will be fit for the trip to Glasgow after limping out of Saturday's 2-0 victory over RB Leipzig -- its second triumph in four days over its title rival after a shootout win in the second round of the German Cup.
Paris Saint-Germain vs Anderlecht: Unai Emery's French heavyweights has cruised through its opening three fixtures -- netting 12 goals with none conceded -- and will be expected to again sweep aside Anderlecht at the Parc des Princes. Edinson Cavani struck twice more in Friday's 3-0 victory over Nice, giving the Uruguayan 15 goals in 14 matches this term, as PSG stayed four points clear in France. Neymar is also set to return after serving a domestic one-match ban following his red card against Marseille. Anderlecht has yet to register a goal or point in this season's group stage, with its last away win in the Champions League proper coming in December 2005.
Atletico Madrid vs Qarabag:
Diego Simeone's Atletico Madrid is still searching for its first win of the competition after a goalless draw in Azerbaijan a fortnight ago. It is in danger of missing out on the knockout stages for the first time since failing to qualify at all in 2012-13. The Spanish side has made a solid start in La Liga and is unbeaten in its first 10 games, but sits eight points adrift of leader Barcelona in fourth place after five draws. Although Qarabag picked up its first Champions League point in Baku, Atletico will be expected to have little trouble in closing the gap on Chelsea and Roma, ahead of a home match against the Italians and a crucial visit to Stamford Bridge.
Roma vs Chelsea: The winner of the clash at the Stadio Olimpico will be well-placed to reach the last 16 with both teams still to play a game against struggling Qarabag. A thrilling 3-3 draw at Chelsea last time out prevented the Premier League champion from moving five points clear at the top of Group C, with Roma now looking for a victory to overtake Antonio Conte's men. Roma won its last home game against Chelsea in the group stages nine years ago, but has not reached the quarterfinals since 2007-08. Chelsea gave its English title defence a boost by beating Bournemouth at the weekend to stay nine points off top spot, while Roma is seven points behind Serie A leaders Napoli with a game in hand.
Olympiakos vs Barcelona: Barcelona could secure a last-16 place on Tuesday. A fourth straight group-stage win in Greece would book a knock-out spot unless Sporting Lisbon beat Juventus. Ernesto Valverde's men are on a 14-match unbeaten run in all competitions since losing both legs of the Spanish Super Cup to Real Madrid. The five-time European champion is flying high in Spain, having only dropped two points in its first 10 outings. Barca talisman Lionel Messi is La Liga's top-scorer so far this term with 12 goals and has also netted three times from three Champions League outings. The first meeting two weeks ago saw Barcelona ease to a 3-1 win with only 10 men , while Olympiakos, bottom of Group D, will be eliminated if it loses and Sporting fail to beat Juventus.
Sporting Lisbon vs Juventus: Sporting and Juventus look set to be in a straight fight for second place in Group D behind Barcelona, with Tuesday's match in Lisbon crucial after the Italians' 2-1 win at Turin . Jorge Jesus' team is looking to draw level on points with its opponent, although last season's runner-up would move all but into the knockout rounds with victory. After winning six consecutive Serie A titles, Juve trails in-form Napoli by three points domestically despite a strong start to the campaign. Jesus is hoping to improve Sporting's European pedigree as the Portuguese giant has not reached the last 16 since 2009, when it lost 12-1 on aggregate to Bayern Munich.
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