Manchester United have threatened to report Real Madrid to Fifa over the Spanish champions’ “totally unacceptable” pursuit of Cristiano Ronaldo as relations between two of the super-powers of European football hit a new low last night.

Sir Alex Ferguson, the United manager, launched a scathing attack on Real last week when he accused the club of having no morals over their brazen courting of the Portugal forward, who has four years left on his contract at Old Trafford. But after Real’s public campaign to lure Ronaldo to the Bernabéu resumed yesterday, the English and European champions took the unprecedented step of issuing a strongly worded statement in which the club threatened to lodge a complaint with Fifa unless attempts to unsettle the player ceased.

“Manchester United has watched with growing irritation the comments attributed to Real Madrid over their alleged desire to sign Cristiano Ronaldo,” the statement read. “The facts are the player is on a long-term contract and his registration is held by Manchester United [and] the player is not for sale.

“The club will have no alternative but to report Real Madrid to the world governing body, Fifa, if it continues to behave in this totally unacceptable fashion. These public attempts to unsettle the player are completely against the regulations and the club will not tolerate them any longer.

“In addition, the club is certain that they are a distraction for the Portuguese national squad as they prepare for the European Championships. No one should be in any doubt that Manchester United will do everything in its power to keep its best players.”

Although Ronaldo has not been an innocent party, fuelling speculation about his future with a series of ambiguous remarks and claiming that a decision will be made on his future next week, United believe that does not excuse Real’s behaviour.

United had previously been reluctant to involve Fifa, mainly for fear of attracting more publicity to the issue, but while some will construe their public condemnation of Real as evidence of their concerns about losing Ronaldo, the club are determined to draw a line under this saga.

Bernd Schuster suggested last week that Ronaldo would move to the Bernabéu “sooner or later” and the Real coach’s claims yesterday that the capture of the player would have as big an impact as the signing of David Beckham, the England midfield player, from United in 2003 were the straw that broke the camel’s back.

Ramón Calderón, the Real president, tried to play down the row last night, while protesting his club’s innocence. “We have not done, nor are we going to do, anything against the wish of a club that we consider a friend like Manchester United. Real Madrid has not done anything wrong,” Calderón said, adding his regret “that a certain discomfort had been created”.

United have no qualms about negotiating with Barcelona, whom Ferguson claimed last week had the class Real, their Spanish rivals, lacked. Gerard Piqué, the United defender, rejoined Barcelona yesterday in a deal worth around £4 million after struggling to make an impact at Old Trafford. Piqué, 21, who has signed a four-year contract with the Catalan club, joined United from Barcelona in October 2004, but made only 14 starts in the ensuing 3½ years.

Mikaël Silvestre could follow him out of the door. The France defender has a year remaining on his contract, but Ferguson cannot guarantee the 30-year-old the regular first-team football that he craves. Laurent Blanc, the former United defender who is in charge of Bordeaux, is keen to take the player back to France.

Louis Saha, the France striker, is also expected to be offloaded and, although it is unlikely that there would be many other departures, John O’Shea, the Ireland defender, appeared to cast some doubt over his future yesterday. Asked whether he was considering leaving, O’Shea said: “That is crossing my mind a lot of the time, but then I think, ‘Where do you go when you leave a team like that?’ That’s an even bigger question. For the time being, I will stay where I am.”