Racing-Métro with be without French international scrum-half Maxime Machenaud for Saturday's crucial Heineken Cup clash with Saracens in Nantes.
The 24-year-old, who has four caps for France, sustained a thigh injury during last weekend's shock 19-15 victory over Top 14 leaders Toulon.
He is expected to be out for approximately two weeks meaning he will also likely to miss the trip to face Munster in Limerick on January 20.
Machenaud should however be fit to feature in the upcoming Six Nations, provided he is included in the French squad set to be named on f=Friday.
Racing are currently two points behind Pool Two leaders Saracens and one point ahead of Munster.
In other news from Paris, French international loose forward Wenceslas Lauret has signed signed with Racing Metro from Biarritz.