On 29 April 2005, a few days after Mikel turned 18, Premier League club Manchester United announced that it had struck a deal with Lyn to sign the player. United's website also claimed that they had done a deal directly with the teenager and that he had signed a contract to join them. Mikel's agents were bypassed as the club persuaded the youngster to sign a four-year contract without representation. Lyn allegedly sent a fax to his agents abroad, claiming their services were no longer required by Mikel. Reports said the deal was initially worth £4 million, and would see the player arrive at Old Trafford in January 2006.
Mikel expressed his delight at joining United in a hastily arranged press conference, where he was pictured holding up a Manchester United shirt bearing the squad number 21. Following his signing of the contract to join United, there were claims from Norway that he had received a number of threatening phone calls from unknown sources. Mikel was assigned a security guard and moved to a safe hotel. On 11 May 2005, however, the midfielder went missing during a Norwegian Cup game against Klemetsrud; he had not been selected for the match but had been watching from the stands. Whilst the player was believed to have left with one of his agents, John Shittu, who had by now flown in to meet Mikel, his disappearance sparked massive media coverage in Norway and also provoked a police enquiry after Lyn Director Morgan Andersen made claims in the Norwegian media that Mikel had been "kidnapped". These claims were later repeated by Manchester United's assistant manager Carlos Queiroz, who accused Chelsea of being involved in the alleged "kidnapping".
It subsequently emerged that Mikel had travelled to London with his agent John Shittu, who was working for Jerome Anderson's SEM group. Manchester United manager Alex Ferguson considered travelling to Oslo to visit Mikel, but decided against this after Mikel was reported to have left the country. Staying in a London hotel and some nine days after disappearing, Mikel stated on Sky Sports News that he had been pressured into signing the contract with United without his agent present, claims furiously rebuffed by both Manchester United and Lyn. Mikel told the British media that Chelsea were the club he genuinely wanted to sign for. In response to these events, United made an official complaint to FIFA about the behaviour of both Chelsea and the player's agents, Shittu and Rune Hauge, already infamous for his role in the George Graham bungs scandal. FIFA dismissed these claims in August 2005, stating there was insufficient evidence to bring a case against Chelsea.
Following the tournament, Mikel failed to return to Lyn, whereupon the club subsequently lodged a complaint with FIFA. On 12 August 2005, FIFA ruled that Mikel should return to Lyn to fulfill the remainder of his contract with the club, whilst they would decide at a later date whether the contract he signed with United should be upheld or cancelled. After a delay of over a month, Mikel complied with the FIFA decision and returned to Lyn in early September 2005 after a three-month absence.
He made his debut for the Nigeria senior team on 17 August 2005, when he came on as a second-half substitute in a 1–0 friendly win over Libya. He did not play for the national team again prior to being named in the squad for the 2006 Africa Cup of Nations. In Nigeria's first group game, against Ghana, Mikel was an unused substitute. However, he was introduced into the second game against Zimbabwe early in the second half. Within ten minutes of coming on, he had supplied both the corner that resulted in Christian Obodo heading the game's opening goal, and scored Nigeria's second goal. He made his first international start in Nigeria's final group game, a 2–1 victory over Senegal.
