Ulster prop Jack McGrath is to undergo surgery on a thumb injury after being ruled out of Friday's Champions Cup game against Clermont Auvergne.
Ulster Rugby say the former Leinster front-rower's "availability to play will be monitored in the coming weeks".
Second row Sam Carter suffered a shoulder dislocation against Bath which will also require surgery and he is set to be out for around three months.
Wing Rob Lyttle will be out for six to eight weeks with a shoulder injury.
McGrath appeared to sustain his thumb injury in the Pro14 defeat by Munster and worsened the problem in the early part of the Irish province's win over Bath in their Champions Cup opener last Saturday.
Eric O'Sullivan was pressed into action for 73 minutes of the victory at The Rec and is set to deputise for McGrath on Friday.
Meanwhile another Ulster squad member, Marcus Rea, suffered a fractured jaw while playing for his club Ballynahinch. He faces approximately six weeks on the sidelines.