Ulster have confirmed they'll be without John Cooney for Sunday's Heineken Champions Cup game away to Northampton.
The kicking scrum-half picked up a calf injury in last weekend's United Rugby Championship defeat to Munster at Thomond Park.
In better news for the province, Robert Baloucoune and Bradley Roberts have returned to the fold for the game at Franklin's Gardens.
Ireland winger Baloucoune hasn't played since sustaining a shoulder injury in Ulster's first European outing of the season - away to Clermont.
Roberts was sidelined at the beginning of December, having picked up a knock in a URC defeat to Ospreys.
A win for Ulster on Sunday will see them bank a place in the last-16. Back-to-back wins in their final two pool games will secure home ties in the next two knockout rounds.
Assistant coach Dan Soper says improvements must be made, however, from their efforts in Limerick last weekend.
"Trying to create momentum in the game, we didn't win that in the middle of the pitch in terms of creating momentum to give our backs an opportunity," he said.
"And at times, when we needed the backs to step up, they didn't quite do that either.
"It's just a lesson that you've got to be on every week in the competitions that we're playing or otherwise you get found out."
Soper added, "If we don't do the job this weekend we fall back into the pack and with your outcome at the end of the pool, you start to rely on what's happening in other fixtures and we don't want that."