Ben Moxham suffered a significant right knee injury in Friday evening's BKT United Rugby Championship defeat to Leinster. He will see a knee surgeon this week.
John Cooney sustained a hamstring injury in the same game and he too is unavailable for selection.
It is hoped that Zac Ward (recent concussion) will re-integrate into full team training later this week and thus be available for selection for the EPCR game against Toulouse on Sunday.
Ulster players who were involved with recent Ireland international duty are back and available for selection ahead of the weekend.