FRANKFURT, Germany (AP) The only sure thing in Group F is that Marseille is already eliminated.
Napoli can advance to the last 16 with a draw or a win at Borussia Dortmund and Arsenal will progress as well if it beats Marseille and Napoli is victorious in Dortmund.
Here are 5 things to know about Tuesday's matches:
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ON THE BRINK
Borussia Dortmund was last season's runner-up after losing the all-German final 2-1 to Bayern Munich but Juergen Klopp's side will be continuing in the less lucrative Europa League after New Year's unless it beats Napoli.
Dortmund is coming off three straight defeats, the first of which was against Arsenal at home, and was beaten 3-0 by Bayern on Saturday, also at home. Dortmund conceded two very late goals.
"I told my players they have five minutes to be depressed, then we have to carry on," Klopp said after his team fell seven points behind Bayern in the Bundesliga.
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NO DEFENSE
Borussia Dortmund's defense is decimated by injuries, with both central defenders Mats Hummels and Neven Subotic on the long-term list and left back Marcel Schmelzer also unavailable.
Newly signed veteran Manuel Friedrich had a solid game against Bayern but he is not registered for the Champions League. Right back Lukasz Piszczek made his comeback against Bayern after six months following hip surgery but he may not be fit yet for the full 90 minutes. Sven Bender may play in central defense, as Sebastian Kehl also lacks match fitness after being nine weeks on the injury list. Neither has played the role much.
Kehl has only three appearances in that position and the last one was in 2005. Bender has played it only once and helped out for a while in the 2-1 loss in Napoli.
Dortmund coach Juergen Klopp could use Koray Guenter, but the Germany under-20 defender's Bundesliga experience consists of a two-minute appearance.
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NO GOALS
Napoli has been outscored 4-0 in its last two Serie A matches, leaving coach Rafa Benitez wondering what happened to an attack that opened the season in solid form.
Diego Maradona's former squad was beaten 3-0 by Juventus two weeks ago then fell 1-0 at home to Parma on Saturday.
Gonzalo Higuain, who was signed to replace the departed Edinson Cavani, is in a scoring lull, and captain Marek Hamsik will miss the trip to Dortmund due to a bruised foot.
Still, Lorenzo Insigne and Belgium forward Dries Mertens have been on form, and veteran Goran Pandev could make the lineup with Hamsik out.
Napoli is third in Serie A.
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ASCENDING ARSENAL
Arsenal had forgotten what being the front-runners felt like. Not only is Arsene Wenger's side top of the Premier League four points in front but it also leads the way in the Champions League.
Although only goal difference has Arsenal ahead of Napoli, confidence is high after winning earlier this month at Borussia Dortmund, last year's beaten finalist.
Arsenal can advance Tuesday with a victory over Marseille if Napoli draws with Dortmund. And Wenger could use Tuesday's game to rest players and give others much-needed game time, including Theo Walcott, who returned from injury after two months out in the 2-0 win over Southampton on Saturday.
"Theo looks a bit off the pace of high level competition, but let's not forget he has been out for seven weeks," Wenger said. "Now he needs competition and preparation, and will go from strength to strength."
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SECOND-STRING MARSEILLE
Marseille will travel to London with a weakened team as wingers Dimitri Payet and Andre Ayew are both out with knee injuries and coach Elie Baup likely to rest key players now that the French side is out of the competition.
Payet scored in Friday's 3-1 win at Ajaccio but then had to pull out of Sunday's training session due to swelling on his right knee. Ayew's injury is more serious and he will be out until the new year after spraining his knee last week on international duty with Ghana.
Marseille is in fourth place in the league and needs to focus on pushing back into the top three, with third-place Monaco five points ahead.
With eight games coming up in 24 days, Baup has already briefed his players that the league is the priority.
"I think everyone's understood that the whole dressing room is going to be involved," Baup said. "We're out of the Champions League ... It might be the chance for some of the young players."
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