Jake White, who coached Smit at Under 21 and senior level with the Springboks, told fans in Port Elizabeth that he felt the South African captain should bow out on a high if his side win the series.
"John has had an amazing career. I suggested he play in the series, win it and then retire," said White.
White also said he expected Smit to be picked at prop and said he was no longer in shape to play at hooker.
"John has seen that he can stay on a bit longer, but it will be difficult to put him at hooker because he's put on a bit of weight. He is not physically in a position to play hooker," added White.