Fijian winger Timoci Nagusa has been ruled out of Ulster's Heineken Cup match against the Scarlets on Friday because of a hamstring injury.
Nagusa was forced the come off during Ulster's win over Connacht and is not in the 25-man squad named on Tuesday.
Irish star Andrew Trimble returns after being sidelined by a hip injury.
Fly-half Stephen Jones, hooker Matthew Rees, wing Mark Jones and scrum-half Martin Roberts are set to return so the Scarlets should be at full strength.
Nagusa's absence is a blow to the province as he had been in fine form.
The 21-year-old wing is Ulster's top try scorer having crossed five times in his last three games. He limped off after 37 minutes and was replaced by Scotland's Simon Danielli.
It was Danielli's first senior competitive outing following knee surgery in the summer and he scored two of Ulster seven tries against Connacht.
Coach Matt Williams has included young Ballymena club man Ian Whitten in the extended squad.
In the forwards, Thomas Anderson returns to the squad and will be hoping to be named in the final line-up which will be announced on Thursday.
Ulster squad - forwards: J Fitzpatrick, R Best, N Brady, T Court, BJ Botha, E O'Donoghue, R Caldwell, M McCullough, K Dawson, R Diack, S Ferris, D Pollock, T Anderson. Backs: N O'Connor, B Cunningham, D Cave, A Trimble, I Whitten, C Willis, I Boss, P Steinmetz, I Humphreys, M McCrea, P Wallace, S Danielli.
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