Three traditional heavyweights - Barcelona, Real Madrid and Bayern Munich - are already through, as are former champion Chelsea, Paris Saint-Germain and Manchester City. Tottenham and Besiktas complete the set of current qualifiers.
A look at what's happening around the Champions League this week:
ATLETICO IN DANGER
Atletico Madrid needs a lot to happen to keep alive its streak of four consecutive appearances in the knockout stage.
Diego Simeone's team, twice a finalist in the last four years, must beat Chelsea away and needs Roma to draw or lose against Azerbaijani team Qarabag at home.
Atletico didn't win any of its first four matches in Group C. Among its setbacks were back-to-back draws against Qarabag.
Sevilla is in a much more comfortable position as it can reach the last 16 for the second straight season with a draw at Maribor on Wednesday. Sevilla can win Group E with a win if Liverpool fails to defeat Spartak Moscow at home.
England is already assured of having two group winners in the last 16, through Manchester City and Tottenham. By Wednesday, it could have five.
On Tuesday, Manchester United needs just a point at home to CSKA Moscow to seal first place in Group A, and already qualified Chelsea can finish top of Group C by beating Atletico.
A day later, Liverpool can secure top spot in Group E by beating Spartak.
The English have never had five teams in the knockout stage of the Champions League.
Germany's representation in the last 16 could come down to just one team, Bayern Munich, after disappointing campaigns from the Bundesliga's best - Borussia Dortmund in particular.
Dortmund, which reached the final in 2013, is already out after failing to win any of its group games and is now competing with APOEL for the consolation of Europa League qualification from Group H. Ahead of its visit to Real Madrid on Wednesday, Dortmund has just two points from five games, the same as Cypriot team APOEL.
Leipzig still has a chance to progress on its European debut but needs a favor from Monaco at Porto in Group G. Leipzig, which is level on points with Porto, hosts group winner Besiktas on Wednesday and will only go through if it secures more points than the Portuguese team.
Bayern hosts Paris Saint-Germain on Tuesday needing to win by a four-goal margin to progress as Group B winner. PSG beat Bayern 3-0 in Paris and has a far superior goal difference.
Germany's fourth team, Hoffenheim, didn't make the group stage after losing in the playoffs to Liverpool.
MORE ITALIAN HEARTACHE?
None of the three Italian clubs in the competition have advanced yet, setting up a nail-biting finish to the group phase that is drawing comparisons with Italy's World Cup playoff loss to Sweden.
Napoli appears to have the toughest path to the knockout stage. Coming off a devastating loss at home to Juventus in Serie A, the Partenopei must win at Feyenoord on Wednesday and hope Manchester City beats Shakhtar Donetsk in Group F.
Juventus, a finalist in two of the last three seasons, can go through with a win at Olympiakos in Group D on Tuesday or if Sporting Lisbon fails to beat Barcelona.
Roma can also go through with a win against Qarabag in Group C on Tuesday, or if Atletico Madrid fails to beat Chelsea.
Amid sluggish ticket sales, Roma coach Eusebio Di Francesco has been urging fans to show up at the Stadio Olimpico.
"We want to win and sing together," Di Francesco posted on social media. "On Tuesday we'll need all of your support."
EXTENDING THE RECORD
After putting seven goals past Celtic two weeks ago in Group B, PSG and its impressive offensive armada of Neymar, Kylian Mbappe and Edinson Cavani will also try to improve what is already a tournament record of 24 goals in this season's group stage.
PSG is seeking a sixth straight group win and to rebound from a shock 2-1 loss to promoted Strasbourg in the French league.
AP Sports Writers Tales Azzoni in Madrid, Andrew Dampf in Rome and Sam Petrequin in Paris, and Associated Press writer Ciaran Fahey in Berlin, Germany, contributed to this report.
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