Springbok captain Jean de Villiers has been withdrawn from the national training camp which starts in Durban on Sunday.
De Villiers was a late withdrawal from the Stormers team for their Super Rugby match against the Cheetahs in Cape Town on Saturday.
He experienced some discomfort in his knee and will undergo a scope in Cape Town on Sunday to determine the full extent of the injury.
As a result, the Springbok selectors have decided to invite uncapped Sharks lock Stephan Lewies to the training camp.
"We've got good depth in the midfield, but due to injury concerns at lock, we've decided to invite Stephan to our camp," said Springbok coach Heyneke Meyer.
"Stephan is playing in his first Super Rugby campaign and has been impressive for the Sharks this year, and was one of their stars on their recent Australasian tour.
"Jean plays a very important role in our team and we decided he should get proper treatment as soon as possible, which will hopefully ensure he returns to the squad sooner rather than later.
"At this stage, we're not sure how long Jean will be out but we will ensure he gets the best medical treatment so that he can play as soon as possible."
The 36 players invited to the Springbok training camp will arrive in Durban on Sunday.
The camp concludes on Wednesday morning, when the players will return to their franchises for the final round of Super Rugby before the June Test break.