Ulster forwards coach Allen Clarke says Ruan Pienaar's departure because of injury before half-time in the Pro12 defeat by the Ospreys is "not a good sign" although there is no further news on the South African's fitness.
Piennar also recently returned to action after a couple of months out because of a knee injury and there will be fears that he has suffered a recurrence of the problem.
Clarke acknowledged that Ulster have a "lot to work on" following Saturday's defeat ahead of the Boxing Day derby against Connacht.
"We've got to look after the ball better. Build some phases and build some momentum," added Clarke.