Bonnaire injury a blow to Clermont's Euro hopes
Toulouse's French lock Romain Millo-Chluski (R) vies for the ball with Clermont's French flanker Julien Bonnaire during the French Top 14 rugby union match betweenToulouse and Clermont on January 5, 2014 at the Ernest Wallon Stadium in Toulouse
The 35-year-old back-row forward is due to be absent for around six weeks after suffering the break in Sunday's 19-12 defeat at four-time European champions Toulouse.
It means he will miss Clermont's last two European pool matches, starting with Saturday's crucial and decisive clash with Harlequins at Twickenham Stoop.
Clermont, runners-up in the competition last season, are four points ahead of Quins at the top of Pool 4 having won three and lost one of their games so far.
But a defeat could see them lose top spot in the group ahead of their final match on January 19 at home to Top 14 rivals Racing-Metro.
The Vulcans will also be without third choice scrum-half Thierry Lacrampe, who revealed on his Twitter account that he has a knee injury which should keep him out for three weeks.
On former France international Bonnaire's injury, Clermont said: "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."
The loss of Lacrampe is perhaps a greater problem for Clermont who already have first choice No.9 Morgan Parra out injured and not expected back until the end of the month, leaving Ludovic Radosavljevic as their only fit senior scrum-half.