Springboks director of rugby Erasmus made the claim on social media.
Vunipola tried to help Cheslin Kolbe off the floor after the South Africa wing had been tackled by Ali Price.
"He seemed to be all right. He played on in the game - so it wasn't that reckless, was it?" said Vunipola.
Erasmus posted the clip on his Twitter account, where he criticised the action of the England prop who had come on as a second-half replacement.