It was reported on Friday morning that 38-year-old midfielder Scholes has told friends he will be quitting the game for a second time next summer. However Ferguson believes the former England international, who was persuaded to come out of a short-lived retirement at the start of the year, would have let him know of any such plans.
Ferguson said: "I would be surprised if Paul had spoken to someone without speaking to me - and he hasn't - so we can dismiss that."
Yet Ferguson said: "Ryan could play for another year or two. Rio has been terrific. The speculation comes from our policy of only giving older players one-year contracts."
Ronaldo will be facing United for the first time since he left Old Trafford in 2009, and Ferguson said, with tongue in cheek: "It is in his contract he can't play against us. It would be a disgrace if he played."
The Scot added: "It will be fantastic to have him back."