When Ince joined United from West Ham in 1989 Ferguson made sure his move was not ended because of a problem with his medical.
Ince told Sky Sports: "I remember the first day that I joined Man Utd. I failed my medical and I thought my move to Man Utd was going to collapse. The way he treated me was like a son and I will never forget that moment.
"To play under that man was so demanding, his standards were so high. We had our ups and downs, a lot have ups and downs with him."
Ince said Ferguson's replacement would have a difficult act to follow.
"It's got to be someone with a massive character. It has got to be someone who can deal with what it takes to be a Manchester United manager.
"Whoever comes in to replace him is going to have to deal with the Man United legacy."