Cesc Fabregas suffered a calf injury during Monaco's goalless draw with Reims last weekend, the club have confirmed.
Fabregas was forced off the field just 15 minutes into Saturday's Ligue 1 clash at the Stade Louis II, with Jean-Eudes Aholou taking his place.
The 31-year-old has started 11 of Monaco's league games since arriving from Chelsea in January, but he is now facing a possible spell on the sidelines and is a major doubt for Sunday's trip to champions-elect Paris Saint-Germain.
No timescale has been put on Fabregas' expected return, with Monaco facing six more matches in their battle to avoid relegation.
Stevan Jovetic also left the pitch early against Reims and it was later revealed that he ruptured his anterior cruciate ligament, meaning an extended spell out of action.