His leadership has been instrumental in helping Ulster to an unbeaten start
Ulster captain Johann Muller suffered a hand injury in last Friday's 19-6 European Cup win over Glasgow at Scotstoun.
A medical scan after the game revealed that he had ruptured ligaments around his thumb.
The veteran Springbok lock had surgery on Sunday to repair the damage and is expected to be out for eight weeks.
Muller would have been an outside bet for a Bok recall - for South Africa's year-end tour to Ireland, Scotland and England - in the absence of the injured Andries Bekker.
However, should Bok coach Heyneke Meyer decide to look at any of the overseas-based locks he is now likely to call on Toulon's Bakkies Botha.
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 Pro12 and the European Cup competitions this season.
His current contract with the Province runs until the end of the of 2012/13 season.