Former All Black fly-half Aaron Cruden tore his calf in Montpellier's 55-13 loss to Lyon last weekend.
The 29-year-old has since been ruled out for a month. The playmaker was making his comeback after two weeks on the sidelines, sustained the injury in the warm-up, but still played an hour of the match.
He will now miss three consecutive Top 14 games, against Toulouse, Perpignan and Toulon, but coach Vern Cotter said he should return in time for the start of the Champions Cup.
“He hurt himself during the warm-up in Lyon, but he played for an hour. In principle, he will be ready for the start of the European Cup,” said the coach.
Montpellier face Edinburgh in their opening game of the European showpiece.