Saracens flanker Will Fraser has been ruled out of Sunday's Heineken Cup semi-final against Toulon with a shoulder injury.
Fraser sustained the injury after 16 minutes against Gloucester last weekend and could now miss the rest of the season.
Mark McCall and his coaching team will now have to make a decision whether to select Jacques Burger or Andy Saull in the vacant openside shirt at Twickenham.
"Will's got an injury to his shoulder and he won't be available to play this weekend," said McCall to the Watford Observer.
"It's a very unusual injury, I can't be very specific on it because we're still exploring exactly what the problem is.
"We need to take advice from some experts before we decide how to handle it and before we know how long he will be out for or whether he'll be out for the rest of the season.
"It's a blow for Will himself more than anything.
"Because he's had a great season and he's played an important part in getting us to the semi-finals of the competition.
"So I'm really disappointed for Will but we've got a number of back-row forwards who are good players and who we trust."