Ulster are set to be without centre trio Stuart McCloskey, Stuart Olding and Luke Marshall for their fixture against the Ospreys this Saturday.
They are all nursing injuries, with McCloskey suffering a foot problem against Glasgow, which keeps him out for a minimum of four weeks.
According to BBC Sport, Ulster's medical staff are also monitoring Olding (groin) while Marshall is being assessed following a head knock.
However, the PRO12 table-toppers could this week be boosted by the returns of Tommy Bowe, Andrew Trimble, Dan Tuohy and Craig Gilroy.
"We will wait to see how they respond to that before finalising our team on Thursday," Ulster assistant coach Allen Clarke told the BBC.