Winger Andrew Trimble could be in doubt for Ireland’s opening RBS 6 Nations championship match against Scotland on Saturday.
The Ulster captain only took part in some of Tuesday’s training pulling out with a tightness in his groin.
Already ruled out are Jonathan Sexton and Peter O’Mahony, with Ulster’s Paddy Jackson set to take the number 10 shirt in place of Sexton for the Murrayfield Stadium match.
Sexton ran as part of his modified training at Carton House yesterday afternoon, but subsequently reported tightness in his existing calf problem.
“We felt it right not to push him through the week and risk potential further damage,” said forwards coach Simon Easterby on Tuesday.
“He’s obviously had a lot of lower limb injuries, a hamstring injury which we’ve managed with Leinster in the pre-Christmas period.
“He picked up a calf problem in the week of the Castres game, only managed 20 minutes in that game.
“As a result of that calf strain and the fact we don’t want to compromise his calf any further. We feel it best to leave him out this week and make sure he’s right for upcoming games.”
Jackson impressed during the Ireland summer tour to South Africa and his form with Ulster this season has been impressive.