It's hard to imagine, but nine-time winner Real Madrid, domestic champions Arsenal and Valencia and defending titlist FC Porto have just one more chance to reach the second round.
Star studded Madrid, an Arsenal team that won the Premier League without losing a game, Spanish champion Valencia and Porto, which won the UEFA Cup and Champions League back to back, are chasing four of the remaining seven places in the last 16 going into Tuesday's and Wednesday's final group matches. German champion Werder Bremen is another team that could lose out.
Nine teams have already qualified -- Italian clubs AC Milan, Inter Milan and Juventus, England's Chelsea and Manchester United, Germany's Bayern Munich, Spanish league leader Barcelona, French champion Lyon and Dutch club PSV Eindhoven.
The draw for February's knockout stage will be made Dec. 17. Third-place teams drop down into the UEFA Cup.
Today is the must-win day for Arsenal, Valencia and Porto, while Bremen only needs a draw to advance.
Arsenal hosts Rosenborg at Highbury needing a win to advance from Group A. Panathinaikos can edge out the Gunners is if they beat PSV Eindhoven in Greece and Arsenal loses. A draw will not be enough for the Greeks, even if Arsenal lose.
The Gunners, which won for the first time in five matches with a 3-0 victory over Birmingham on Saturday, will be without influential midfielder Patrick Vieira and defender Lauren through suspension.
"When things are bad, you have to dig in and come out of it. You can't perform all the time and be one of the best on the pitch," Arsenal striker Thierry Henry said. "But when you play for Arsenal, everyone expects you to win -- no matter what."
Manuel Almunia could start again in goal after displacing Jens Lehmann on Saturday. The Spaniard kept Arsenal's first clean sheet in 14 matches, but didn't have a lot to do. Lehmann had played in all of Arsenal's 49-match unbeaten league streak.
Group H is the only group where all four teams could reach the next round. Chelsea is certain of the top spot, with Paris Saint-Germain, Porto and CSKA Moscow fighting for second.
PSG can assure itself of staying in second place by beating CSKA Moscow in Paris. CSKA will progress if it beats PSG and Porto doesn't beat Chelsea. Porto can qualify if it beats Chelsea in Portugal and PSG draws or loses.
Jose Mourinho returns to Porto after guiding the club to the Champions League title last season. He's likely to rest several players in preparation for the top-of-the-table league clash with Arsenal next Saturday.
Mourinho has also called on extra security for the match after he was spat at during Chelsea's 3-1 win at Stamford Bridge.
Porto will be without defender Nuno Valente and midfielder Raul Meireles.
"It will be a decisive game for Porto and knowing Jose Mourinho like I do, even though Chelsea are in he will not make things easier for us," striker Maciel Cunha said.
In Group G, Inter Milan is already through and will only finish second if it fails to beat Anderlecht -- which has yet to earn a point -- and Werder Bremen wins in Spain.
Valencia has to beat Bremen by more than one goal to earn second place over the Germans on goal difference. Valencia beat Albacete 1-0 on Saturday to extend its unbeaten run to five matches. In Group F, AC Milan and Barcelona are already through. Celtic, which hosts AC Milan, needs to match or better Shakhtar's result to secure third place. Shakhtar hosts Barcelona.