Loosehead prop Steven Kitshoff has been ruled out for four weeks after picking up an injury while training with South Africa.
The in-form Stormers front-rower has damaged the medial ligaments of his left knee.
Scans on Wednesday confirmed a grade two MCL injury which is estimated to keep Kitshoff out of the Springboks' next three matches including this weekend against the World XV.
"We wanted to use him off the bench with Vincent Koch (against the World XV) to see what impact they could make," said South Africa head coach Heyneke Meyer on Wednesday.
With Kitshoff now unavailable the Springboks are likely to use Tendai Mtawarira and Trevor Nyakane against the Wallabies, with the pair involved at Newlands on Saturday.