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.

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