Marseille lost goalkeeper and captain Steve Mandanda to an ankle injury as their six-match winning run in Ligue 1 was snapped following a 1-1 draw at struggling Metz.
France international Mandanda limped off on 32 minutes to be replaced by Yohann Pele, who conceded the opening goal at the Stade Saint-Symphorien when Opa Nguette scored just before half-time.
The 37-year-old Pele produced a superb save to keep out Habib Diallo's second-half penalty before Nemanja Radonjic salvaged a point for Marseille with an equaliser on 70 minutes.
Andre Villas-Boas' side remain four points behind leaders Paris Saint-Germain, who have two games in hand and travel to Saint-Etienne on Sunday.
"It will be important to rebound with a victory against Nimes (next Saturday) because we lost two points tonight," said Villas-Boas, who downplayed the severity of Mandanda's injury.
"I think it won't be too serious. We'll see, the ankle isn't too swollen. I hope it's nothing too bad and he will be there for Nimes."