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With the European Cup back under lock and key at Old Trafford, Manchester United are preparing for a battle to keep their trophy player from the clutches of Real Madrid. Even in his finest hour, Cristiano Ronaldo was alarmingly evasive about his future, strengthening the belief that he will push for a move to Spain unless United agree to make him the best-paid player in the world.

Moments after his team had emerged triumphant from a nerve-shredding penalty shoot-out against Chelsea on Wednesday night, a breathless Ronaldo told an on-pitch reporter that “I want to stay” at United. But, swaggering out of the Luzhniki Stadium 90 minutes later, proudly wearing his Champions League winner’s medal around his neck, he said that he could not make any promises about his future and repeated that a decision will be made in the next two weeks.

Sources have indicated that Ronaldo and Jorge Mendes, his agent, will push for a significant increase on the £120,000-a-week contract he signed only 13 months ago, citing the willingness of Real, either this summer or next, to pay him more than £150,000 a week, in addition to approving a world-record transfer fee in excess of £50 million.

Mendes is reported to have held discussions with Predrag Mijatovic, the Real sporting director, in Moscow on Tuesday and, even though David Gill, the United chief executive, again tried to dismiss fears of losing Ronaldo yesterday, the club are likely to be unnerved by some of the winger’s post-match comments.

Asked whether he could assure United supporters that he would stay next season, Ronaldo said: “I never promise nothing. I don’t promise nothing to my mum. I don’t promise nothing to the supporters. I want to stay, I want to stay, but the future no one knows.”

Asked whether this meant that his future would hinge on discussing a new contract, he said: “I don’t know nothing. No one speaks with me. Two weeks. Not this week. I will know the following week. I don’t say I will make a decision. I say the club make a decision.”

If the ball is in United’s court, Ronaldo will see out the remaining four years of his contract, but Ramón Calderón, the Real president, demonstrated his growing optimism by suggesting that the 23-year-old would be able to engineer a move to Spain if, as they believe, that is what he desires.

“The players play where they want,” Calderón said. “If a player decides to leave, he is unstoppable. Slavery was abolished a long time ago. I have always said that if Manchester want to sell him, we will ask about him and if he wants to come, we can pay what they ask.”

Bernd Schuster, the Real coach, believes that Ronaldo will play for the Spanish champions at some point in his career. “Sooner or later, Cristiano Ronaldo will wear the white shirt,” he said. “I hope that it is when I am still at the club.”

According to Marca, the Spanish sports daily, Ronaldo said that his future “will be known next week and everyone will be happy”. It would appear that United cannot take his long-term future for granted.