Manchester United privately conceded defeat to Chelsea last night over the transfer of the teenager John Obi Mikel after a day of extraordinary intrigue in Norway and London.

United will reserve the right to pursue the matter with Fifa and the club were still insisting last night that they had an agreement with the 18-year-old Nigerian.

So concerned were United at the involvement of agents claiming to act for the champions that Alex Ferguson was yesterday morning preparing to make a personal visit to Mikel's club, Lyn, in Oslo. Instead, it is believed the midfielder was on a British Airways flight from the Norwegian capital to Heathrow at 7.30am after absconding from a cup match, prompting Lyn to contact police over his disappearance. Mikel failed to report for training yesterday and again did not contact his club.

That left United downcast about their chances of enforcing the contract Mikel signed with them on April 29th, admitting that if Chelsea want the player enough, they will be powerless to prevent him moving there. If their fears are realised, it would be a breathtaking move from Chelsea.

United attempted to save face by issuing a public statement of defiance, warning that litigation could follow. "We remain confident we have reached an agreement with Lyn Oslo and the player, both of which are signed," said the club's communications director Phil Townsend. "We believe he has signed for us." The intrigue grew as quotes attributed to Mikel, a player Jose Mourinho has described as "pure gold", stated that he no longer wants to join Manchester United, prompting Old Trafford to make informal contact with the Premier League on the issue, but United were yesterday awaiting developments before making drastic moves.

The player's club were even less clear about an increasingly muddled situation. "We do not know where John is," said Lyn's sporting director Morgan Andersen. "He has been taken away by agents who told us they were working for Chelsea."

Andersen has claimed privately that Chelsea's involvement in the player's career stemmed from a £170,000 payment to fund the academy at which Mikel and three other Nigerian players were trained. On making the payment, Andersen claims, the club were promised by agents that they would be provided with first refusal on the players.

Chelsea made a formal offer to Lyn that did not meet their valuation, opening the door to United.