Nick Williams and Wiehahn Herbst will not be included in Ulster's squad as the province continue to count the cost of their bonus point win over Scarlets in last weekend's European Champions Cup.
The tighthead prop and number eight both hobbled off the pitch with hamstring injuries and because of the swift turnaround for the return game in Wales will not participate in the fourth round match.
Irish centre Stuart Olding suffered concussion in the game and was replaced at half-time by Stuart McCloskey, who damaged elbow ligaments in a second half collision.
It’s Olding’s third concussion this year but there remains a slim chance that he will play as he adheres to the return to play protocols.
McCloskey will not be involved in the return fixture, which makes Luke Marshall's return to fitness all the more important for coach Neil Doak.
Loose forward Franco van der Merwe also suffered a concussion in a clash of heads with Williams. It is his first concussion of the season and his inclusion will also come down to how he responds to the return to play protocols.
