Montpellier lose All Black pivot
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 flyhalf in the Montpellier squad.
When Cruden was sidelined with a thigh injury in October, ex-Scotland coach Cotter either used scrumhalf 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.
Agence France-Presse
