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 No 8 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."
Gloucester boss Nigel Davies was delighted with his team's display as they brought the curtain down on their home games this season.
"We showed elements throughout our game today that we have seen bits of this season," he said.
"If we become more consistent in certain basics of our game, then this team is very capable. The players were fantastic, the crowd was superb and everything came together.
"We played good territory throughout the game and put pressure on Saracens in their half, and because of that we were in control for large periods.
"But Saracens are a quality side who could well go on and win Europe this season, so for us to put in a performance like that and get the result is pretty significant.
"Heineken Cup qualification was one of the priorities at the start of the season, and we have also shown progress with this group of players."