Prop BJ Botha made his second appearance for the province since returning from international duty. He was sprung from the bench for the second half in Galway.
But the South African injured his wrist and came off three minutes from the end, with youngster Paddy McAllister taking his place.
A statement from Ulster Rugby explained: "At this stage it is too early to put a timescale on the length of lay-off for each player, and treatment and resassessment will be ongoing with a view to their return to rugby."
The player himself said: "The injury feels like it's starting to heal. The X-ray and scan suggest I will be in pain for a while, but I'll hopefully be back in no time."
Botha's injury is understood to be the more serious of the two. He joins fellow props Declan Fitzpatrick (torn calf) and Adam Macklin (broken ankle) on Ulster's early season injury list.
Ballynahinch clubman Jerry Cronin, who has been included in Ulster's Heineken Cup squad, could be called on to make the step-up to senior provincial level.