Gene Fairbanks is a major doubt for the Brumbies' must-win Super 14 match against the Waikato Chiefs in Hamilton on Friday.
The inside centre is having scans on a torn hamstring after his side's crucial 37-15 victory over the Blues on Saturday.
He will be a big miss for the Brumbies, whose late charge towards the semi-finals will end if they do not claim a bonus-point win.
Coach Andy Friend told the Canberra Times: "It's a big blow to us and I thought Gene was very good for us (against the Blues).
"But I think we've got the depth and the medical advice we've had so far is not overly positive."
Stirling Mortlock could return to his favoured centre position if Fairbanks is ruled out of the match.
In a further injury blow, Mitchell Chapman has been told by club doctor Warren McDonald he will not be fit to play after the lock had to spend the night in hospital on Saturday recovering from concussion and was still ill on Sunday.