Springbok lock Victor Matfield will miss the Springboks' Test against Argentina in Pretoria on August 16 due to injury.
Matfield is suffering from a small tear in a cartilage after being sent for scans on Tuesday after feeling some discomfort in his knee at training on Monday.
He was seen by an orthopaedic specialist in Pretoria and will be unavailable to face los Pumas.
"Victor's injury will initially be treated conservatively and a decision on his further participation in the competition will be made during the course of next week," said Springbok team doctor Craig Roberts.
The other injury concern at this stage in the Springbok squad is Jean de Villiers, who is returning from a knee injury he sustained during Super Rugby in May.
"We'll only know at a later stage if Jean will be ready to face Argentina next week in Pretoria," said Springbok coach Heyneke Meyer.
"In Victor's case, we will have to call up a short-term replacement, which we'll announce as soon as possible.
"Jean is our captain and one of the most experienced players in the squad.
"We'll give him as much time as possible to recover; however, replacement cover can be called up if he is ruled out of the Test at Loftus Versfeld."