Any remaining goodwill between Manchester United and Chelsea vanished yesterday when the dispute over the transfer of John Obi Mikel's transfer descended into open hostility. United confirmed they have lodged an official complaint with the Premier League, and Alex Ferguson's assistant Carlos Queiroz accused the champions of "taking football into the jungle".

Despite persuading Mikel to sign a contract a fortnight ago, United have privately given up all hope of the Nigerian midfielder playing for them after what they claim is "the dirtiest of dirty-tricks campaigns".

Chelsea are understood, however, to have made an important breakthrough in determining that Mikel is free to join them.

Several agents are acting on their behalf and a document has been uncovered that allegedly states the Norwegian club Lyn had no sale rights for the player.

Mikel is in London, speaking to representatives acting on behalf of Chelsea, and Queiroz believes the 18-year-old has been offered a financial incentive that would multiply his wages by "three or four times".

Even seasoned campaigners such as Ferguson, a man who has been accused of skulduggery in the past, have been genuinely taken aback, particularly as the London club are preparing for next week's Premier League hearing into their meetings with Arsenal's Ashley Cole, and at a time when they have also been accused of trying to tap Rio Ferdinand.

"This is not a new movie. It has happened with Rio Ferdinand, Ashley Cole and now John Obi Mikel," Queiroz added. "The important thing is that the football institutions - the people at Fifa, Uefa and the (English) Football Association - are strong and united on this issue and help to keep the game with credibility and respectability.

"We must present a strong team and condemn who is in the wrong here. And if we allow people who don't deserve to be in football to damage the credibility of the game, we all lose.

"I lose as a professional, the players lose, and the public, everybody loses. We need to keep the business of football under rules and moral principles, otherwise football will drop into the jungle."

Ferguson is understood to have instructed Queiroz to present United's case in the strongest possible terms, starting with Mikel's allegation that he had been unfairly pressured into moving to Old Trafford from Lyn.

United are convinced he had been advised to say that to begin the lengthy and complicated process of breaking his contract to move to Stamford Bridge.

They hold Chelsea, chief executive Peter Kenyon in particular, responsible.

"We have a boy here who is 18 and talking on television in Norway a few days ago about how happy he is to have signed a contract at Manchester United," Queiroz added.

"It is wrong, but very easy, that another club should then come along to this contracted player, sell him illusions and promise him three or four times the money he has already been offered.

"It is unacceptable that a boy of 18 can almost be kidnapped from his home environment and taken to London and, within one day, be talking on TV with an unhappy face."