Just after the 23-minute mark at the Stade de France, Curry could be heard on the referee’s microphone alerting official Ben O’Keeffe to a comment possibly made by Mbonambi at a ruck.
“Sir, if their hooker calls me a white c***, what do I do?” Curry inquired of O’Keeffe.
“Nothing, please,” responded the official, before adding a few moments later, “I’ll be on it,” in what may have been an unrelated comment. The alleged incident itself could not be heard on the television broadcast.
The sport’s governing body has now confirmed that it will be investigating the incident.
“World Rugby takes all allegations of discriminatory behaviour extremely seriously,” the organisation said in a statement.
"We can confirm that we are formally reviewing the allegation made by England’s Tom Curry in relation to the use of discriminatory language during the England versus South Africa Rugby World Cup 2023 semi-final on Saturday.
“World Rugby will not be making further comment until the conclusion of the process.”
South Africa face New Zealand in the World Cup final on Saturday night.
Mbonambi, who ended the game as the Springboks captain after the substitution of Siya Kolisi, is the only specialist hooker in South Africa’s squad.
He played the full 80 minutes in the semi-final, with Deon Fourie, ostensibly his bench back-up, introduced in the back row.
A statement from South Africa Rugby released on Sunday said: “We are aware of the allegation, which we take very seriously, and are reviewing the available evidence.
“We will engage with Bongi if anything is found to substantiate the claim.”