Chris Henry and Ruan Pienaar look certain to remain out of action for Ulster on Saturday after missing the European win over Oyonnax last weekend.
Ulster’s director of rugby Les Kiss said on Tuesday that Henry would miss the Pro12 trip to Italy to face Treviso because of his shoulder problem.
Kiss added that influential scrum-half Pienaar is “likely” to be missing again as he recovers following a virus.
Stuart Olding is expected to be play his first Ulster game in 10 months.
Ireland centre Olding has been out since last March after suffering his second anterior cruciate ligament injury in two seasons.
However, he made his return to playing duty for Ulster A last weekend and managed to score a try in the British Irish Cup defeat by Bristol.
Olding has suffered a series of serious injuries in recent years.
He missed most of the 2013-14 campaign after rupturing his anterior cruciate ligament.
The Ulster back suffered two serious injuries last season as an elbow injury which ruled him out from January to late March was immediately followed by another anterior cruciate ligament injury as he made his comeback to action in a Pro12 game against Cardiff Blues.