The Daily Mail says there is growing belief around the club that a deal for Ronaldo is not as fanciful as it sounds.
United have already launched what amounts to a feasibility study to see if they could finance the biggest player purchase in their history — one manager Sir Alex Ferguson estimates would run into "hundreds of millions".
After watching Ronaldo score twice against Barca on Tuesday to take his total for Madrid to 185 goals in 183 games, the United boss knows he is one of the few players who would be worth it.
Ferguson left the door open to a return when asked about Ronaldo in December, saying: ‘You never know. He may want to go to another club at some point and I’d hope he would want to come here.
"I’d love to see that but it’s fanciful thinking really. First of all, there’s how much it would take to get him from Real and, secondly, I don’t think there’s any chance they would want to sell him."