Evans has since emerged as a summer target for Manchester City after spending two seasons at The Hawthorns, leading former midfielder Robson to reveal that the Northern Ireland defender would be an inspired purchase for Pep Guardiola.
"Jonny Evans is a real good player," said Robson, according to talkSPORT.
"I was surprised when we allowed him to leave, especially for a fee of £6m. There is no way I would have allowed Jonny Evans to leave this football club.
"He is a great lad, he is a really honest boy, he works really hard in training and he has done a great job for West Brom.
"If you are manager of any football club, Jonny Evans is the type of character you want in your football club."
Evans made 131 appearances for United before being sold under Louis van Gaal.