Will Fraser is a major doubt for Saracens' Heineken Cup semi-final against Toulon after suffering a shoulder injury in the loss to Gloucester.
The flanker was forced off after just 15 minutes of Sarries' 28-23 Aviva Premiership defeat at Kingsholm and faces an anxious wait before discovering whether he will play again this season.
"Will is going to go for an MRI scan, and we will know more after that," said Saracens director of rugby Mark McCall.
"It would be a big loss. He has had a great season, but we have got some decent back-rowers to cover."
Saracens' six-game unbeaten Premiership run came to end after Jonny May scored two first-half tries and England number eight Ben Morgan claimed a superb solo score to confirm Heineken Cup qualification for Gloucester.
"It wasn't maybe the performance that we wanted," added McCall, after centre Joel Tomkins scored two tries and his midfield partner Owen Farrell kicked 13 points.
"Gloucester put us under some pressure from time to time. We gave away a couple of reasonably soft scores - some of our mistakes gave Gloucester their opportunities.
"We were 25-16 down, but arguably we could have won that game at the end. We fought our way back into it. The nature of our fightback and the spirit and togetherness is what we are about."