"When players first come to the club you don't know enough about them [to see whether they're captain material], it's only in the last few years that I've seen that with Rio," explained the United boss.
"He had a casualness about him when he first joined as a young lad which sometimes frustrated you, but he's matured and has a great strength of character.
"He's a good leader now and I think he will be our captain when Neville and Giggs hang their boots up."
Despite seeing Ferdinand substituted late on in England's victory over Ukraine with a groin problem in midweek, Sir Alex remains hopeful he will be fit to face Aston Villa on Sunday.
"He didn't train on Friday, but we hope he will on Saturday," revealed the boss. "He's got a good chance for Sunday, although if he does play he may be struggling by Tuesday. However, the important thing is to get him ready for Sunday."