Ulster's All Black centre Paul Steinmetz has been ruled out of Saturday's Celtic League clash with Glasgow at Ravenhill on Saturday because of a knee injury.
Steinmetz has not long reeturned from a fractured jaw but the latest setback is not thought to be serious. He has fluid on the knee.
Second row Matt McCullough is also a doubt with a back injury.
"In the Celtic League it's all about generating a number of wins in a row," said coach Mark McCall.
"There are 10 games remaining, and a lot can happen in that time.
"We have two home games in the Celtic League starting with Glasgow on Saturday, and then the Scarlets later in the month."