The South African picked up the issue midway through their game against Connacht.
Ulster have confirmed that back-rower Juarno Augustus will be out for a number of weeks with an ankle ligament injury.
The South African picked up the issue midway through their 29-24 victory away to Connacht in the URC last weekend.
It rules him out of Friday's visit of Munster to Belfast - Iain Henderson Rob Herring are also doubts for that game.

Tuesday Morning Sports Update
Lossiemouth Wins Today's Feature At Leopardstown's December Hurdle
Ciarán Frawley Signs Two-Year Deal With Connacht
Racing Action Comes To A Close At Leopardstown Christmas Festival Today
Monday Morning Sports Update
Stephen's Day Soccer Update
Stephen's Day Racing Schedule