The West Brom captain is currently the subject of a failed £18m offer from Manchester City.
Robson, who made the move the other way, from West Brom to United in 1981, and is still a “global ambassador" at Old Trafford, thinks releasing Evans in 2015 was a mistake by Louis van Gaal.
“Jonny Evans is a really good player," he told Talksport. “I was surprised when we allowed him to leave especially when the fee was £6million, to go to West Brom.
“There is no way I would have allowed him to leave this football club."
That echoes the thoughts of Sir Alex Ferguson, who gave Evans his United debut as a teenager.