Manchester United have lodged an official complaint with FIFA over Real Madrid's relentless pursuit of Cristiano Ronaldo.

United warned the Spanish giants in a statement released on May 27 that they would consider reporting them unless they ended their public campaign to take the winger to the Bernabeu, but the level of speculation surrounding the Portugal international's future has intensified since then.

"On 27 May, Manchester United made clear its intention to report Real Madrid to FIFA if it continued to involve itself in the future of Cristiano Ronaldo," a statement read on Monday. "Unfortunately, Real Madrid has not kept its own counsel and the club feels it has no alternative but to make a formal complaint to the world governing body, which it has done."

The statement continued: "The precise content and nature will remain confidential."

A FIFA spokesman told PA Sport: "I can confirm that we have received an official request from Manchester United to look into the matter.

"We have only just received the documents so we need some time to analyse them before we can make any decision."

FIFA's regulations do not stipulate any possible sanction against Real Madrid but they do say one club have to inform another if they are to start negotiations with their player.

The rules do not specifically state however that the club that owns the player have to give consent.

Article 18 of FIFA's regulations for the status and transfer of players states: "A club intending to conclude a contract with a professional must inform the player's current club in writing before entering into negotiations with him.

"A professional shall only be free to conclude a contract with another club if his contract with his present club has expired or is due to expire within six months. Any breach of this provision shall be subject to appropriate sanctions."