Ferguson: Rio not first choice
Ferdinand has lately suffered a dip of form, probably because of recurrent injury problems. The signing of Phil Jones has seen his playing time reduce even further.
Talking before United's Champions League clash against Otelul Galati, Ferguson explained the situation to the media.
"I explained to Rio that, simply, we have two young centre halves coming through."
"I'm really happy to have the four of them and I hope to keep the four of them for a long time, but Rio is obviously 33 now and he's obviously lost the yard of pace he had five years ago."
"That doesn't mean to say he can't play the game in a different way - where he used to rely on his place he doesn't do that now, he can't do that now. That's obvious," Ferguson added.
"We've all faced that decisive moment in our careers where you realise you have to change your game. I did it myself as a player when I lost that real sharpness, and Rio will do the same and he'll be fine."