Four teams have already qualified for the last 16 ahead of matchday five of this season's Champions League group phase. On Tuesday, Chelsea can also clinch progress with just a point in Switzerland, while Arsenal could wrap up qualification too.
FC Basel (SUI) v Chelsea (ENG)
Knocked out in the group stage last season as the defending champions, Chelsea need just a draw against Basel in Switzerland to clinch their place in the last 16, and a fourth successive win in Group E will see the Blues advance as winners of the section. Chelsea won at St Jakob-Park last season in the semi-finals of the Europa League but will be wary of the Swiss champions, having lost 2-1 when they met in London in September. Chelsea come into the game fresh from a 3-0 win at West Ham United that left them in third place in the Premier League. They have lost just one of their last 13 games in all competition, while Basel remain clear at the top of the Swiss Super League and have lost just once in 19 outings.
Steaua Bucharest (ROM) v Schalke 04 (GER)
Schalke come into matchday five in second place in Group E, and a win in Romania coupled with a defeat for Basel against Chelsea will see the Bundesliga club through to the knockout stages. The Royal Blues were comfortable 3-0 winners when the sides met in Gelsenkirchen in September but they can be infuriatingly inconsistent and threw away a two-goal lead before needing a late Benedikt Hoewedes equaliser to earn a 3-3 draw at Eintracht Frankfurt in the Bundesliga on Saturday. Coach Jens Keller described that result as "maddening". He is still without long-term injured Klaas-Jan Huntelaar for the visit to the Romanian capital to face a Steaua side who are unbeaten domestically but without a win in Group E.
Arsenal (ENG) v Marseille (FRA)
Arsenal will look to close in on a place in the last 16 by inflicting a fifth defeat in five games in this season's competition on Marseille. If the Gunners win at the Emirates Stadium, they will qualify for the last 16 should Borussia Dortmund fail to win at home to Napoli. A draw will be enough if Dortmund lose. Meanwhile, Marseille are already eliminated but could yet steal third place and a Europa League berth with the right combination of results. That seems unlikely, though, especially with coach Elie Baup having fitness concerns over Andre-Pierre Gignac and Mathieu Valbuena. Premier League leaders Arsenal - who won 2-1 in southern France in September - welcomed back Theo Walcott after injury in Saturday's Premier League victory over Southampton.
Borussia Dortmund (GER) v Napoli (ITA)
Last season's beaten Champions League finalists Borussia Dortmund could be eliminated with one round of group games still to play if they fail to beat Napoli in Germany and Arsenal beat Marseille. Such a threat is very real for Jurgen Klopp's team, who suffered a shattering 3-0 home defeat at the hands of Bayern Munich in the Bundesliga on Saturday as they struggle to cope with a defensive injury crisis. Neven Subotic, Mats Hummels and Marcel Schmelzer are all sidelined. Napoli beat Dortmund 2-1 in Italy and a win here will seal their place in the last 16. However, they also come into the game on the back of a disappointing domestic result at the weekend, a 1-0 home loss to Parma damaging their title prospects in Serie A.
FC Porto (POR) v Austria Vienna (AUT)
Two-time European champions Porto need to win at home to Austria Vienna at the Estadio do Dragao as they chase Zenit for second place in Group G and a spot in the last 16. The Portuguese side won 1-0 in Vienna in September thanks to a second-half Lucho Gonzalez goal but have taken just one point in their subsequent three matches, losing at home to Zenit and Atletico Madrid. Paulo Fonseca's side are undefeated in their domestic league just now and sit top, but were held to a 1-1 draw at home by Nacional on Saturday, leaving the pitch at full-time to jeers from their supporters. Those fans will not tolerate another slip-up against an Austrian side who have registered just one point in Group G so far and failed to score a single goal.
Zenit St Petersburg (RUS) v Atletico Madrid (ESP)
Atletico are already through to the last 16 as the only side apart from defending champions Bayern Munich to win their first four group games. Diego Simeone's side are already certain to finish first in Group G too, so the Argentine coach has rested key players for the trip into a Russian winter, Diego Costa and David Villa among those left at home. The clash with Zenit comes on the back of a stunning 7-0 win against Getafe that kept them in contention at the top of La Liga. Zenit have only won once so far in the group and were beaten 3-1 in Madrid in September, but a win at the Petrovski stadium will take them through to the last 16 should Porto fail to win later on Tuesday.
Ajax (NED) v Barcelona (ESP)
Remarkably, Barcelona's 4-0 win against Ajax in September was the first ever competitive meeting of two European giants linked by iconic former player and coach Johan Cruyff. Now they meet in Amsterdam for the first time, with Barcelona already through to the last 16 and needing just a point to be sure of winning Group H. The Catalans - who are top of La Liga - are without a host of injured players just now, including world player of the year Lionel Messi and goalkeeper Victor Valdes. Ajax beat Celtic in their last group game to keep alive their chances of progressing and come into this match fresh from a 3-0 win against Heracles in the Eredivisie at the weekend.
Celtic (SCO) v AC Milan (ITA)
This tie at Celtic Park is a crunch encounter in the race for the second qualifying spot in Group H. Milan head to Glasgow in second place and will be through if they win and Ajax lose at home to Barcelona. However, the Rossoneri are a club in crisis just now, their 1-1 weekend draw with Genoa leaving them in the bottom half of Serie A and sparking protests from angry fans. Celtic are bottom of the group but they are a formidable prospect at home and beat Milan 2-1 in Glasgow's East End in the group stage of the competition in 2007. A repeat this time would take the Hoops above Massimiliano Allegri's side in the standings.