Erasmus even mentioned the possibility of fielding one of his coaches against Wales this weekend if they get a late injury crisis.
Former number eight Duane Vermeulen is among the last-resort options for the Test in Cardiff.
Vermeulen, 39, retired with 76 Test caps after the World Cup final in Paris two years ago.
“We kind of rolled the dice because we really only have 24 players with us,” said Erasmus.
“Ntuthuko Mchunu is the 24th player, and Duane Vermeulen is currently the 25th if we get an injury before Saturday.”
Thirteen of Wales’ squad have returned to their English and French clubs, Steve Tandy’s side having conceded half-centuries to both Argentina and New Zealand this autumn with his first-choice line-up.
“Both teams were in a similar situation with regards to the availability of players, but they have a balanced squad with a few seasoned players and several younger guys who will be desperate to make a statement,” said Erasmus.
“So, we are expecting them to come out firing and to throw everything at us.”
