The timing of David Gill's departure as Manchester United chief executive, described as a "big loss" to Sir Alex Ferguson, is bound to intrigue others. The club are 12 points clear at the top of the Premier League, have an enticingly poised Champions League last-16 tie with Real Madrid to complete in a fortnight and are safely into the quarter-finals of the FA Cup. As Gill, who hopes to join Uefa's executive committee in May, steps away with a second treble looming into view, aged just 55, many wonder, why now?

He is the one man at Old Trafford who can argue with Ferguson. The Scot alluded to the healthy "tension" in their working relationship when he said: "David has been a magnificent chief executive. Of course we have had a million arguments, but I have always enjoyed them because I know that David has two great qualities: he is straight and always puts Manchester United first. No disagreement is ever personal with him.

"Him stepping down is a big loss to me but the fact that he is staying on the board encourages me that the reason for his departure is heartfelt, that he believes it is time for the club to move on. If I could have found a way of persuading him to stay I would love to have done that."

Gill's explanation was that it is time for United to move on. He said: "I am also of the view that all businesses need to refresh themselves with new management and ideas and after 10 years in charge I believe it is appropriate for someone new to pick up the baton."

Gill's strong alliance with Ferguson helped him add to his mountain of trophies. He was the man in charge when the Glazers bought the club and since becoming, in 2003, Ferguson's "boss", as the Scot called him in a leaving eulogy, Gill has overseen the winning of four Premier League titles, three League Cups, one European Cup, one Club World Cup and an FA Cup.

Yet Gill also had to weather near hatred from United supporters over the highly controversial leveraged deal triggered by the Glazers in their 2005 takeover when club assets were used to mortgage the finance required by the Americans. In 2010 Gill said of the movement of fans who wear the club's former colours to signify their disquiet with the Glazers: "The green and gold campaign and the momentum behind that can get a bit tiring.

"We understand people's desire to protest and I think it is a minority. Would we prefer not to have them [green and gold scarves]? Yes. They have a right to protest. A lot of the fans clearly care about the club and that is a strength. I think that [the green and gold] minority will go away."

His support of the Glazers, though, was a U-turn on the position Gill offered when opposing their buyout as "overly aggressive" and "unmanageable", stating in 2004 that "debt is the road to ruin".

On Twitter, United supporters @Dillscan wrote of Gill: "Sold fans down the river by supporting Glazers. Good riddance". But @jamesu87 said: "I think he gets a bad rep for having done a wonderful job in tough circumstances."

An argument will now run that Ferguson has lost a powerful ally as Gill preceded the owners at United – joining as finance director in 1997 – while his replacement, Ed Woodward, is a Glazer man having helped broker their deal when he worked at JP Morgan before joining them at the club following the takeover.

Woodward's prime role with Ferguson will be "facilitating transfer activity", according to the club. How competent Woodward, who has a BSc in physics from Bristol University, proves in this area and his ability to develop a good working relationship with Ferguson will determine his effectiveness in the job.

As Gill said of the 40-year-old whose business background is accounting and banking, Woodward's has been a steep learning curve in the vagaries of the national game. "I have worked with him for more than seven years and in that time he has built up knowledge of football matters, which will hold him in good stead for the future," Gill said.