Duane Vermeulen will miss the third Test with Ireland after the South Africa number eight was ruled out with an elbow injury.
Vermeulen is one of five players struggling for fitness within the Springboks squad and joins Pat Lambie in definitely missing the series decider in Port Elizabeth.
The 29-year-old sustained his elbow problem in the opening 40 minutes of the second clash with Joe Schmidt's side and scans have revealed the extent of his injury.
"Duane went for a MRI/CT scan on Monday, which revealed a grade two injury in the elbow," said team doctor Konrad von Hagen.
"He will be out for between two to six weeks, depending on how the injury responds to treatment."
No replacement will be called up for Vermeulen, but they have concerns over Warren Whiteley, Trevor Nyakane and Damian de Allende.
Whiteley - who could replace Vermeulen - sustained a shoulder injury on Saturday, and was able to train on Monday but refrained from any contact drills.
Further assessments will take place on Nyakane's swollen ankle after x-rays showed no fracture, while De Allende missed Monday's session due to a stomach bug.