Marseille midfielder Mathieu Valbuena will undergo tests on Monday to determine the severity of a back problem sustained in Sunday's 1-0 Ligue 1 defeat at Bordeaux.
The 28-year-old France international was replaced by Fabrice Apruzesse in the 73rd minute at the Stade Chaban Delmas, after suffering a spasm in the back.
OM coach Elie Baup said on French television channel Canal+: "He was hit. I hope it's not serious."
Valbuena added: "In my last action, I felt something. I do not want to accelerate. I prefer not to take risks. We'll see after the tests. I hope to return as soon as possible."
Yoann Gouffran scored the only goal of the game seven minutes into the second half as Les Girondins moved up to second - a point above OM - in the standings.
Baup was disappointed to be heading back to Marseille empty-handed.
"This is an opponent who did not look like troubling us," he told OM's official website.
"The match was very balanced, with both defences strong. Both teams were solid, well organised. We had opportunities with Andre Ayew, and strikes from distance."
He added: "We have a game in hand but it is never good to lose points against a direct rival."