Marseille captain Mamadou Niang faces six weeks on the sidelines after suffering a collarbone injury.
The 30-year-old striker sustained the knock during L'OM's 3-1 UEFA Champions League home defeat at the hands of Real Madrid on Tuesday.
Niang clashed with Spain goalkeeper Iker Casillas in the second half and had to be replaced in the 69th minute.
To make matters worse for Marseille, the defeat meant Madrid qualified from Group C to leave the French side in third, forcing them to settle for a place in the Europa League.
Niang will certainly miss the Ligue 1 games against Boulogne, Lorient, St Etienne and Auxerre, although because of the French winter break, he could only be absent for four games if he makes a quick recovery.
Marseille are currently seventh in the French top-flight with 25 points from 14 games and are six points off leaders Bordeaux.