Ferdinand accepts some players are easier to replace than others.
He said: "I have always said it, Paul Scholes is my favourite player.
"He is one of the top two players I have ever played with. It is his decision to stop and you have to respect that.
"When Roy Keane and Ruud van Nistelrooy left for instance, we didn't get like-for-like replacements.
"We got different players who had a great impact."