South Africa's World Cup title defense suffered a major blow on Thursday when hooker Malcolm Marx was ruled out for the remainder of the tournament with a long-term knee injury.

"Marx, who was not included in Springbok coach Jacques Nienaber’s matchday squad to face Romania in Bordeaux on Sunday, went down at training on Wednesday after having his knee caught in contact," the Springboks said in a statement.

"With the Springboks having the luxury of an enlarged 33-man squad in France for the international showpiece, and sufficient cover at hooker within the squad, he will not be replaced in the squad at this stage."

Nienaber said that while the Springboks, who beat Scotland 18-3 in their Pool B opener, were now left with only one specialist hooker in the squad, other players could step into the role if needed.

"First and foremost, we are extremely disappointed for Malcolm, and we wish him all the best in his recovery,” he said.

"We have enough cover at hooker with Bongi (Mbonambi) and Deon (Fourie) in the squad, while Marco (van Staden) has also been training there and has been named on all our team sheets so far as a hooker option."