Luke Marshall ruled out for six weeks after thumb surgery
Centre Luke Marshall is likely to be unavailable for Ulster's two opening European Champions Cup games after being ruled out for around six weeks.
Marshall underwent surgery on Friday to repair ligament damage to a thumb.
Ulster begin their Pool 1 campaign against French side Oyonnax on 14 November, followed by a home game against Saracens on Friday 20 November.
Robbie Diack is set to miss Friday's home match against the Cardiff Blues because of a muscle tear in his thigh.
Second row Dan Tuohy may also be a doubt after suffering concussion during the 16-10 defeat by Edinburgh at Murrayfield last week.
The Ireland lock will follow the return to play protocols before a decision is made about his availability.
Meanwhile an update on the fitness of long-term injury victim Stuart Olding is expected next week following a review with his surgeon.
Olding suffered an anterior cruciate ligament injury at the end of March and is expected to be out of action until at least Christmas.
After the visit of the Blues to Kingspan Stadium at the end of this week, Ulster face testing away trips to Munster and the Dragons.
The Irish province lies fifth in the table after home victories over Ospreys and Treviso, but losses on the road against the Scarlets and Edinburgh.