Erasmus said Mapimpi might also have a fractured cheekbone.
South Africa beat Tonga 49-18 in their final pool game to move to the brink of the quarter-finals. The defending champions have to wait for the match between Ireland and Scotland on Saturday to be certain of a place in the last eight.
The 33-year-old Mapimpi was a Rugby World Cup winner with South Africa in 2019 but came to this tournament as a backup to first-choice wings Cheslin Kolbe and Kurt-Lee Arendse.
Am was also a key part of the Springboks’ 2019 triumph and set up the first try of the final against England for Mapimpi.
Am and Pollard initially missed out on this year’s World Cup squad because of injury but were among a group of players put on standby. Am was back in training after recovering from the knee injury he sustained in August, the Springboks said.
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