Iain Henderson will miss Ulster's United Rugby Championship game against Edinburgh on Saturday because of a hip issue with Luke Marshall, Jake Flannery and Rob Herring also ruled out.
Ireland lock Henderson sustained his injury in Ulster's defeat by Glasgow last weekend.
Marshall injured a shoulder in the same game where fly-half Flannery was a late withdrawal because of a groin issue.
Ireland hooker Herring remains out because of a calf injury.
The Ulster medical update released on Friday morning detailed that Ethan McIlroy (facial fracture and concussion), Sean Reffell (ankle), Angus Curtis (concussion), James McCormick (shoulder), Marcus Rea (elbow), Callum Reid (back), Michael Lowry (hip) and David McCann (ankle) remain unavailable for this weekend's game at Kingspan Stadium.
The statement added that the fitness of Dave Ewers, Nick Timoney, Stewart Moore, Jude Postlethwaite, Greg Jones and John Andrew for selection is being considered following their recent injuries.