Greek side Olympiakos delivered a blow to Marseille's hopes of reaching the last 16 of the Champions League by beating them 1-0 in their Group F clash here on Wednesday.
A well-taken 82nd-minute goal by substitute Ioannis Fetfazidis, brilliantly picked out by Spanish midfielder Fran Yeste, was enough to keep alive the battle for the second qualifying spot from the group.
Arsenal clinched top spot with a 2-1 win over Borussia Dortmund, leaving Marseille still second but just a point ahead of Olympiakos, while Dortmund are three points adrift.
The German champions are due to host Marseille in the final match, while Arsenal visit Olympiakos.
"This has been a really bad week," said Marseille coach Didier Deschamps.
"It was a bad team performance all round, I won't even go into the individuals most at fault. I don't like losing.
"Obviously, it is a huge disappointment with regards to the importance of the match."
The first half was a poor affair, with the visitors creating what chances there were. Veteran Swedish defender Olof Mellberg actually had the ball in the net but it was ruled out for offside.
French international goalkeeper Steve Mandanda saved his side in the 36th minute after Mathieu Valbuena lost possession in his opponents' half.
While Valbuena flapped his arms in disgust, Giannis Maniatis made good ground unopposed and unleashed a shot that Mandanda beat out, only for Jose Holebas to recoup the ball, and his effort was heading for the top corner after taking a deflection but the Marseille shot-stopper somehow get a hand to it.
Marseille were more ambitious in the second half and created two excellent chances to break the deadlock.
France midfielder Valbuena sneaked in at the near post but his effort from three yards out was a tame one and it hit the arms of goalkeeper Balazs Megyeri and went out for a corner.
His fellow French international Alou Diarra was also denied by Megyeri as he ran in unmarked at the far post but his header across goal was kept out by a one-handed save from the Hungarian.