Manchester United finance director Nick Humby and commercial director Andy Anson have resigned.

The Old Trafford outfit confirmed the news to staff today before making a formal announcement that both men, who have formed a key bridge between the previous PLC board and the new ownership structure under Malcolm Glazer, will leave in February to take up fresh challenges.

As two of only three non-Glazers heavily involved in the running of United, the departures of Humby and Anson would appear to isolate chief executive David Gill, although there is no belief Gill has any plans to leave himself.

Nevertheless, the move has come as a blow to Gill, who has worked closely with Humby since his arrival at United in 2002 and was responsible for appointing Anson in February 2004.

Both men have had success in major recent projects, with Humby responsible for delivering the new stadium expansion on time and Anson heavily involved in negotiations over new shirt sponsors, which secured a record £56.5million deal with American banking giant AIG.

"I am very disappointed to lose Nick and Andy," said Gill. "Nick has been an excellent finance director at the club for the last five years, getting involved in all areas of the business.

"His final major project has been to manage successfully the stadium expansion in time for the start of the current season.

"In his three years at the club, Andy has set a new commercial strategy on which he has delivered excellently. He has played a lead role in our record shirt deal with AIG, as well as the negotiations to restructure our platinum partnerships and media businesses."

While both men have been eager to stress how much they have enjoyed working at Old Trafford, particularly lifelong United fan Anson, there is bound to be speculation over the precise reasons for their departure.

At the time of the Glazer takeover last year, the pair, along with Gill, were seen as essential in maintaining continuity and providing specific business expertise in the football industry, something the new owners clearly lacked.

However, the increasing involvement of Malcolm Glazer's sons Joel, Avie and Bryan from the family's base in Florida is bound to have undermined Humby and Anson to an extent, even if there has been no actual fall-out.

United have already begun the search for successors in both positions, although it has been suggested now the club is in private hands there is no requirement for a wide-ranging finance director in the mould of Humby.

Representative of fans' group Manchester United Supporters Trust (MUST) - formerly Shareholders United - who bitterly opposed the Glazer takeover, have urged Humby and Anson to "come clean" over their departures and let Red Devils supporters know what is happening at the club.

"Now is the time for them to come clean, do the honourable thing and let the supporters know what is going on behind the scenes at our football club," said MUST spokesman Sean Bones.

"At the time of the takeover, Joel Glazer said he would speak to the supporters. They have not done so, which is a shame because we have a lot of questions for them to answer."