Sam Allardyce resigned as Bolton Wanderers manager yesterday to pursue a new challenge, feasibly at Manchester City or Newcastle United, after suspicions over his future plans led the club to bring forward his planned departure at the end of the season.

Allardyce informed Phil Gartside, the Bolton chairman, on Friday that he intended to leave the club and take a sabbatical after eight years in charge at the Reebok Stadium. Gartside suspected that he had lined up another job and even contacted City officials to ask whether this was the case before reluctantly deciding yesterday to accept his resignation with immediate effect and to replace him with Sammy Lee, his assistant.

Lee’s appointment could be confirmed as early as today, but Allardyce’s future is less clear. His prospects of landing the City job, occupied at present by Stuart Pearce, appear to be largely reliant on a takeover bid by Ray Ranson, the club’s former player. Ranson’s hopes of gaining power at the City of Manchester Stadium remain in the balance, however, with two consortiums — one American and the other led by Thaksin Shinawatra, the deposed Prime Minister of Thailand — preferred by the club’s board.

Newcastle, meanwhile, have yet to make a decision on Glenn Roeder’s future as manager. Allardyce rejected the job in 2004, but is certain to be among the contenders if Roeder is dismissed. The Tyneside club have also shown interest in Sven-Göran Eriksson, the former England head coach, as revealed by The Times this month. Senior Newcastle officials last night distanced themselves from a bid for Allardyce’s services.

Sources close to Allardyce have indicated that he would be interested in the Newcastle job and also that of City, in the event of a takeover, but also that, as with Alan Curbishley’s resignation at Charlton Athletic a year ago, he would welcome a period away from the game if the right opportunity does not arise.

He has endured a difficult past 12 months, not only suffering the disappointment of missing out on the England job, but also having his name tarnished by a BBC Panorama documentary that alleged corruption involving Bolton’s dealings with his son, Craig, who was working as an agent.

In a statement, Allardyce said: “The decision to leave the football club, which has been my spiritual home for over 18 years, as both player and manager, is one of the hardest decisions I have had to make in my life. It was mutually decided that I step down now rather than at the end of the season, to give my successor the ideal opportunity to experience the preparation and build-up of match day in readiness of next season.”

Gartside said: “I have reluctantly accepted the resignation of manager Sam Allardyce after eight years of unprecedented success at the club. I would like to thank Sam for his enormous contribution both as a player, but more importantly as a manager. He has given his reasons, which are private, and we respect that privacy.”