Ulster will be without Luke Marshall when they face Glasgow Warriors on Friday, after he picked up a concussion in their last outing.
The 25-year-old centre has previously suffered a string of similar injuries, including four concussions in one year.
According to Ulster, he will miss out on Friday’s PRO12 Round 4 game and will continue to be assessed while following the return-to-play guidelines.
The team currently has a string of players out injured and confirmed on Tuesday that Andrew Trimble’s expected return to action has been delayed due to a slight foot injury.
Craig Gilroy and Jacob Stockdale both look to be a couple of weeks away from playing due to toe injuries, while Kyle McCall is a doubt for the next game after a side abdominal injury in training.
A number of other players are either continuing with rehab or resuming full training with a view to getting back in action.
Among them are Dan Tuohy and Tommy Bowe, who are both hoping to be available for selection soon, as they recover from right ankle and right knee injuries respectively.
Full back Louis Ludik scored the opening try in the Scarlets game.
He expects a tough game against Glasgow on Friday night.
Performance analyst Niall Malone says he is conscious of the threat posed by winger Tommy Seymour, who was part of the Ulster setup earlier in his career and his international teammate Stuart Hogg, who has scored important tries against Ulster in previous games.