David Beckham has declared that Cristiano Ronaldo should stay at Manchester United rather than pursue his supposed “dream” move to Real Madrid - but, even as the Spanish club acknowledge that it may be “impossible” to sign him this summer, details have emerged of the sums that they are prepared to offer to prise him from Old Trafford.

Sources in Madrid claimed last night that Ronaldo, who earns £120,000 a week at Old Trafford, would be offered a contract worth almost £150,000 a week after tax to join Real. That would make him the best-paid player in world football by some distance, with Real having also indicated that they are prepared to shatter the world transfer record and offer United a fee in the region of £75million to get their man. Real officials have also claimed that discussions over Ronaldo - presumably with his representatives or another third party - have been taking place for the past 12 months, another claim that will infuriate United.

United maintain that there will be no deal, regardless of Real's and even Ronaldo's feelings on the matter, but there is concern at Old Trafford that his head may have been turned by Real's interest. In theory, they may be willing to offer him a new contract if that is what it takes to keep him in Manchester, but, so far, there have been no such negotiations with him or his agent, Jorge Mendes, which is why United are alarmed by Ronaldo's repeated claim that he is about to make an announcement on his future.

Beckham, who preceded Ronaldo in the United No7 shirt before enduring four, largely difficult, years at Real, entered the debate yesterday, suggesting that the 23-year-old should stay at Old Trafford. “It's none of my business, but I believe he's at the right club and a club he should stay at because, as much as Real Madrid are a great team and one of the biggest clubs in the world, he's only just starting at Man United,” Beckham said. “He has only been there a few years. He has a lot of people around him who will protect him. As a fan of Man United, I hope he stays there, but who knows?”

Ramón Calderón, the Real president, appears to have backed off slightly since David Gill, the United chief executive, wrote to him last week urging him to drop his bid, but even yesterday, in acknowledging that it may be “impossible” to agree a deal for Ronaldo, he made clear the depth of his and his club's commitment to signing the Portugal forward.

“At the moment, it seems impossible for him to come,” Calderón said. “We have to think that, whatever Cristiano says, Manchester won't want to sell him. We don't know if Ronaldo wants to leave or not. That seems to me to be getting ahead of events.

“So much has been said that we don't know if it's true that he wants to leave. We don't know if he will say nothing or if he will say something different. If he says something different, Manchester will have to act and, if they want to negotiate with Madrid or another club, they will do so. There are many circumstances which must come together.”

Real are prepared to sell players such as Mahamadou Diarra, a former United target, and Robinho, the 24-year-old Brazil forward, to accommodate Ronaldo. Robinho even claimed that he is aware of proposals from Chelsea and United - the latter a supposed swap deal involving Ronaldo - but neither Gill nor Sir Alex Ferguson would entertain such a plan. United are far more interested in adding to their squad, but their hopes of signing Karim Benzema, the Lyons forward, remain distant. Luis Fabiano, of Seville, remains a more feasible alternative, but that deal may hinge on the outcome of a dispute over his contract.