South Africa international Heini Adams said he will be out of action for four to six weeks due to a broken wrist.
The Bordeaux-Begles scrumhalf was injured in last Saturday's 21-20 win over Top 14 champions Castres.
Adams had scans on his wrist on Sunday and was wearing a brace on Monday, explaining that he would need at least a month on the sidelines while the brace will remain for a week.
Meanwhile, New Zealander Matthew Clarkin will miss Wednesday's visit of Montpellier and Sunday's trip to Grenoble but should be fit to face Oyonnax on September 14, his coach Rafael Ibanez said.
The No.8 came off against Castres with a broken nose but does not need an operation.