Ulster will be without Andrew Trimble and Craig Gilroy for Saturday's Champions Cup match against Clermont Auvergne at the Kingspan Stadium (1.0). Jared Payne (kidneys) is a long-term injury victim.
Trimble damaged his ankle while playing for Ireland in their victory over Australia while Gilroy picked up an injury in Ulster's excellent victory over the Cardiff Blues at the Arms Park last weekend.
Both players would be doubtful of regaining fitness in time for the return game in France on Sunday week.
Ulster coach Les Kiss will have the fillip of the returning Paddy Jackson and Rory Best, who were rested for the Cardiff match after their exploits with Ireland. Kiss explained: "Craig Gilroy won't make it. Trimby will be short too, he won't make the match. That sort of challenges us. We know the story with Jared. We do have Rory and Paddy back.
Massive difference
"Robbie Diack is fine. Alan O'Connor we're just monitoring because he had a concussion a few weeks ago so we're just doing the right thing. Those two [Jackson and Best] make a massive difference. We're not relying on that.
“The rest have to do their job and make it easy for them. They’re in a great vein of form. They had a good November, especially Besty. It was an enormous campaign from him. He stood up big and tall and got some real reward.”
Ulster’s South African-born prop Wiehahn Herbst, who signed a new two-year contract extension on Wednesday with the province that will keep him there until the summer of 2019, has been drafted into the Champions Cup squad as an additional player having recovered from injury recently.
He replaces short-term signing, Georgian Anton Peikrishvili who was injured throughout his stay before moving on. Herbst becomes Irish qualified next year.