Manchester United have insisted they may report Real Madrid to FIFA over their public pursuit of Cristiano Ronaldo.
The Premier League and European champions issued a statement on Tuesday evening describing their 'growing irritation' at continuing comments seemingly emerging from the Spanish club concerning their interest in the Portugal attacker.
The statement said: 'Manchester United has watched with growing irritation the comments attributed to Real Madrid over their alleged desire to sign Cristiano Ronaldo.
'The facts are: the player is on a long-term contract and his registration is held by Manchester United; 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.'
Madrid coach Bernd Schuster confirmed Ronaldo is his club's number one summer transfer target.
United boss Sir Alex Ferguson has already voiced his dislike of Madrid touting for Ronaldo, pointing out their major domestic rivals, Barcelona, refrain from public expressions of admiration for other clubs' players.
That tactic has worked for Barca in securing the services of United defender Gerard Pique on a four-year contract on Tuesday.
But with any softly-softly approach for Ronaldo almost certain to meet with failure, Real have decided to come out all guns blazing.
And Schuster's latest comments seem to have prompted a curt response from United on Tuesday.
Ferguson is sure to be infuriated by Schuster referring to the 23-year-old in a manner that would suggest the signing has virtually been completed.
'There are other players we have been looking at but everything has slowed down a little due to all this Cristiano Ronaldo business, seeing as he is the big priority for the club,' said Schuster.
'The English way has been a perfect education for a player with such exceptional individual talent.
'There he has learned to enjoy his football as a complete professional. This means we would get a Cristiano who would arrive here with his lessons learned.'
Given such a statement, Ferguson is probably glad he is due to embark on his annual summer holiday next week, thus avoiding what is sure to be a regular stream of stories linking Ronaldo with a move to Madrid.
For his part, the United boss is adamant Ronaldo neither wants to, nor will be, leaving Old Trafford this summer, claiming last week the acid test of the relationship between player and club will not be faced for another two years.
By that time, Ferguson expects his team to have added at least one more European Cup to a tally they took to three with their penalty shoot-out win over Chelsea in Moscow last week.
In addition, they could have overtaken Liverpool's record of 18 English championships; United moving to within one with their latest success, the 10th of Ferguson's 23-year stint as manager.
Not that Real are likely to be dissuaded by history.
Although they, like United, have won back-to-back titles, European success has remained frustratingly out of reach since 2002 for the nine-time winners, a record Schuster is determined to put right with Ronaldo leading the charge.
'Cristiano would help us in a lot of ways, without a doubt, but we can't stop with just him,' he explained.
'He'll be expensive and we'll have to pay a lot of money, but we need more players because he won't be enough.
'For a few months now we have had a plan and we know what we want, but now Alexander Hleb has been added to that plan.
'We didn't know he would be able to leave Arsenal, but now it seems he will.'
Gunners boss Arsene Wenger will be about as happy with Schuster as Ferguson but the German, who has impressed at Real since replacing England boss Fabio Capello at the end of last season, is not likely to be influenced by that.
He certainly does not see the man expected to be confirmed as the world's best player in December being a problem to his squad, no matter what massive price tag is attached and what attention he attracts. After all, this is the club that signed David Beckham.
'In this Madrid side, the kid wouldn't create any problems,' he said.
'For the fans this signing would be an amazing explosion similar to what happened here when Beckham arrived.
'This isn't England, and that change will affect him. We have to be clever about this and sort this problem out for the kid.'