A medical scan after the game revealed that he had ruptured ligaments around his thumb.
He had surgery on Sunday to repair the damage and is expected to be out for eight weeks. Capped 26 times by South Africa, Muller has played 50 times for Ulster and has been club captain since August 2011. His leadership has been instrumental in helping Ulster to an unbeaten start in both the RaboDirect PRO12 and the Heineken Cup this season.
His current contract with the Province runs until the summer of 2013.
Guinness PRO12
Suite 208, Alexandra House,
The Sweepstakes
Ballsbridge, Dublin 4, Ireland
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