Ulster's Paddy Jackson is expected to be out of action for about six weeks after sustaining a shoulder injury in Friday's win over the Ospreys.
The fly-half was forced to retire hurt after 63 minutes of his side's 25-16 win at the Kingspan Stadium.
On Monday Ulster revealed that the 22-year-old international had suffered an AC joint sprain.
Jackson was left out of Ireland's squad for the autumn internationals against South Africa, Georgia and Australia.
He missed Ireland's summer tour to Argentina with a back injury and had to sit out Ulster's Pro12 success over Glasgow in Belfast last month after suffering concussion.
Meanwhile Michael Allen, who is capable of playing at centre or on the wing, has recovered from a dislocated shoulder and will come into the reckoning for Friday's Pro12 game away to Munster.