Ulster centre Darren Cave has been ruled out of action for up to six weeks because of a ligament injury.
The 24-year-old twisted a foot during the 41-7 win over Leicester at Ravenhill on Friday night.
It is a blow for Ulster ahead of Saturday afternoon's crucial Heineken Cup Pool 4 game against Clermont Auvergne in France.
The Irish province currently lead the pool on 19 points, with Clermont three points behind on 16.
Ulster will look to secure their first win on French soil this weekend.
A win for Ulster would ensure that they top their group and qualify for a home tie in the quarter-finals.
A losing bonus point may be enough to ensure their passage to the last eight, although that would depend on other results going their way.
Munster and Leinster have already qualified for the quarter-finals.
"The manner of the win over Leicester shows that we have the experience and quality to move in the right direction," said Ulster Director of Rugby David Humphreys.
"There is a real buzz about the place and the players we have now are as good as any that have pulled on the Ulster shirt for a long time.
"I rate Clermont as the top team in Europe in terms of the depth and quality of their squad, and they have a wonderful home record.
"It will be a huge test for us, but if we play as we did on Friday night, we have a great opportunity of going there and causing an upset.
"If we do, the prize of a home quarter-final awaits us," enthused the former Ulster and Ireland fly-half.