Lions loose forward and Springbok squad member Cyle Brink picked up a knee injury at training in Durban on Thursday.
The nature of the injury is not yet known, but the 24-year-old was seen in the Bok team hotel on Thursday afternoon wearing a brace on his right leg and hobbling around on crutches.
Brink was not named in the Bok squad for Saturday's Rugby Championship opener against Argentina at Kings Park, with Erasmus instead opting for the Bulls' Marco van Staden as his loose forward cover off the bench.
But with Erasmus looking to build a pool of players between now and the 2019 World Cup, he was keen to get Brink involved in one of the first two matches of the Championship.
The Boks are yet to release a medical statement, but he will leave the squad on Thursday night and it now seems impossible that he will be part of next weekend's trip to Mendoza to take on the Pumas.
Kick-off on Saturday is at 17:05 .
15 Willie le Roux, 14 Makazole Mapimpi, 13 Lukhanyo Am, 12 Andre Esterhuizen, 11 Aphiwe Dyantyi, 10 Handre Pollard, 9 Faf de Klerk, 8 Warren Whiteley, 7 Siya Kolisi (captain), 6 Francois Louw, 5 Pieter-Steph du Toit, 4 Eben Etzebeth, 3 Frans Malherbe, 2 Malcolm Marx, 1 Tendai Mtawarira
Substitutes: 16 Bongi Mbonambi, 17 Steven Kitshoff, 18 Thomas du Toit, 19 Marvin Orie, 20 Marco van Staden, 21 Embrose Papier, 22 Lionel Mapoe, 23 Damian Willemse