The Red Devils manager dismissed rumors linking the forward with a second spell at Old Trafford this summer.
The Portugal international has been heavily linked with a move back to his former club at the end of the season amid uncertainty over his future with the Spanish side.
The 28-year-old will make an emotional reappearance at Old Trafford this week in a Madrid shirt when the two clubs meet in the Champions League, but Ferguson has described the prospect of Ronaldo becoming a Manchester United player again as "false hope" and feels the forward is likely to sign a new deal with Madrid.
“There hasn’t been anything to encourage me to think Cristiano would come back here," Ferguson told reporters. "As far as I am aware, there is nothing in it at all. Ronaldo has got two years left on his contract, and it seems to me it is all part of the negotiations that are going on about a new deal.
“Maybe his agent is playing the game. I think it is false hope."
United hosts Real Madrid in the second leg of their Champions League round of 16 tie on Tuesday, after the first leg in Spain ended in a 1-1 draw last month. Even though Ronaldo scored the equalizing goal for Real Madrid and provides a threat to eliminate the Red Devils from the competition, Ferguson believes that he will receive a warm welcome from the Old Trafford faithful.
"Cristiano will get a good reception," Ferguson said. "All our former players, especially the ones who have been great for this club, get a good reception when they return."