Former New Zealand fly-half Aaron Cruden suffered a knee injury during Montpellier's 36-26 European ChampionsCup victory over Glasgow on Saturday.
The French Top 14 side said the 28-year-old would have an MRI scan on Monday to find out how long he will be out of action.
"I'm not going to say anything but I hope it's not too bad. I'll wait until tomorrow to find out more," said Montpellier coach Vern Cotter.
Cruden was injured in the 68th minute after a tackle from Matt Smith and was replaced by scrum-half Enzo Sanga.
The former World Cup-winner is the only specialist senior fly-half in the Montpellier squad.
When Cruden was sidelined with a thigh injury in October, ex-Scotland coach Cotter either used scrum-half Benoit Paillaugue or youngster Thomas Darmon in his absence.
Montpellier are second in the Top 14, two points adrift of league leaders La Rochelle, and play third-placed Lyon next Saturday.
