Marx, one of the world’s best hookers, suffered the injury in training ahead of the Springboks’ second pool fixture against Romania.
The 29-year-old had not been due to feature in that game, but was likely to be South Africa’s starting hooker for the remainder of the tournament.
The Springboks have elected not to replace Marx in their 33-man squad “at this stage”.
“First and foremost, we are extremely disappointed for Malcolm, and we wish him all the best in his recovery,” said head coach Jacques Nienaber.
“He’s been working very hard to be in the best form possible for the tournament, and it’s tragic that his campaign has ended this way. As a team we will remain in contact with him, as we do with all injured players such as Lukhanyo (Am), Handre (Pollard) and Lood (de Jager), and support him as much as we can through the recovery process.
“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.
“We’ll assess our needs for the rest of the tournament and confirm who we are calling up as an additional player later this week.”
Mbonambi starts and captains South Africa against Romania in Bordeaux this weekend, with Fourie, more often an openside flanker at club level, covering from the bench.
Joseph Dweba is the hooker on standby should Nienaber and director of rugby Rassie Erasmus decide a replacement is required.
The loss of Marx is an undoubted blow to the defending champions.
He and Mbonambi’s complementary skills have dovetailed superbly for much of the last half-decade, with Marx an excellent ball carrier and breakdown operator.
Fourie’s elevation to the second spot in the hooking pecking order also comes as a risk, with the 36-year-old yet to scrummage at test level.
“I’ve never tasted it (playing hooker) at test-match level, that’s the reality,” Fourie admitted this week. “I’ve been training there for two years now with the Boks.
“I’ve been in and out with hooker training, but hopefully it’s like riding a bike. If I get the opportunity to play there I can just jump back on and ride it.”
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