Starting in the Springboks' inaugural victory last Sunday in Marseille against Scotland (18-3), Marx, 29, was injured Wednesday in training while he was not to participate in the second match of his team Sunday in Bordeaux against Romania.
"He has worked very hard to be in the best possible shape for the tournament and it is tragic that his adventure is ending like this," South African coach Jacques Nienaber said in a statement.
The South African staff is giving themselves until the end of the week before announcing the name of his replacement in the group of 33 players for the rest of the competition.
"We will assess our needs for the rest of the competition before confirming the identity of the one we will call as an extra player later in the week," Nienaber explained.
Bongi Mbonambi, starter at the 2019 world title in Japan, will logically move up the hierarchy at the position of hooker, which also covers the versatile third lines Deon Fourie and Marco van Staden.
Marx (1.89 m for 117 kg), hooker with 64 caps, is a centerpiece of the Boks with whom he won the world title in 2019.
His forfeit is another blow for South Africa, already forced to do without centre Lukhanyo Am, opener and striker Handré Pollard and second row Lood de Jager.
Hit in the shoulder against Scotland, second row Eben Etzebeth is unavailable for seven to ten days.
After Romania, the weakest opponent in Group B and crushed (82-8) by the Irish in its first match, the Springboks will face Ireland, first nation in the world ranking, on September 23 at the Stade de France.
A meeting that could decide the potential opponent of the XV of France in the quarter-finals.
© 2023 AFP