Clermont Auvergne captain Julien Bonnaire has been ruled out of action for six weeks with a fractured arm.
That means he will miss Saturday's crunch Heineken Cup clash with Harlequins at the Stoop.
The former France international, 35, suffered the injury in Sunday's 19-12 Top 14 defeat at Toulouse.
Clermont are four points ahead of Quins at the top of Pool 4 and defeat could see Quins leapfrog them into top spot going into the final match of the group stage.
The French giants confirmed: "This injury does not need an operation but will force the Clermont flanker to have his arm immobilised for several weeks and will keep off the pitch for a period estimated at six weeks."
Watch Harlequins take on Clermont live on Sky Sports 2 on Saturday, with coverage from 1.35pm.