The Portuguese, who is tipped to win the Ballon d'Or, admitted in July he "missed" the Old Trafford outfit amid strenuous speculation regarding a Santiago Bernabeu exit.
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"He was one of the most dialled people on my phone at the time! But I think the opportunity has gone now," Ferdinand is quoted as saying by the Daily Mirror.
"If we could have done it, I think it would have been last summer. He’s signed a new deal at Real now.
"As footballers you don’t really let on too much to each other. It’s like a chess game. And in those situations you have got your one and two first-choice moves or scenarios that you want to happen.
"So to let people know is sort of letting the cat out of the bag. You play your cards close to your chest. But if he was going to leave Real Madrid, I think Manchester United would have been the place he would have come to."
Ronaldo will find out if he is Fifa's World Player of the Year on Monday - ahead of four-time winner Lionel Messi and Franck Ribery - and Ferdinand has backed his former team-mate to be crowned.
"We had a debate about it in training, and I think he has been the best in the calendar year, definitely, he’s the best," he said. "Look at his goals! He’s scored more goals than some clubs have in the calendar year.
"He is a great model to any young player to look up to. He got to being World Player of the Year back in 2008 and he wasn’t satisfied.
"Ronaldo has gone on again to another level and he should have won it a couple of seasons ago when Real Madrid won La Liga.
"He wants to become the best player in the world again. He’s still got people doubting him - maybe there’s a jealousy element to it - and he wants to prove them people wrong. That’s how you become the best."