Manchester United chief executive David Gill will step down from his position with the Premier League leaders at the end of June.
Gill, who will remain on the United board, has been chief executive for a decade and has given United 16 years of service since his arrival as finance director in 1997.
The 55-year-old, who is also a vice-chairman of the FA, is standing for election to UEFA's executive committee in May. Executive vice-chairman Ed Woodward will take over Gill's duties at Old Trafford.
Gill has been a close ally of Sir Alex Ferguson and the United manager paid tribute to him, saying he has done a "magnificent" job and lamenting his departure.
He told United's official website: "I have been at United for over 26 years and for 23 of those years my boss has been one of only two men: Martin Edwards, who brought me to the club, and David Gill. I have enjoyed working with both.
"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 he always puts Manchester United first. No disagreement is ever personal with him. He always wants the best for United, whether it's the players, the training ground or the staff.
"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. But he has made his decision and I respect him for it.
"He has been, and will continue to be, a fantastic success for Manchester United. He has all the qualities of successful people ingrained in him: energy, honesty, integrity, personality and decision-making ability. I wish him well in whatever new challenges he will tackle in the future."
Gill added: "It has been the greatest privilege to serve Manchester United for 16 wonderful years – the last ten of which as its chief executive. I have worked alongside the finest manager in the history of the game and been part of what I consider to be the best club in the best sport in the world.
"It has been a very hard decision because I love this club and, as the fans' banner says, it is 'more than a religion'. I've experienced some incredible highs, such as the Treble in 1999 and the league and Champions League double in 2008, and lows, like losing the title with the last kick of the season last year. But that is what makes this club and this sport so compelling.
"However, I have always been conscious of the fact that, as a member of staff, I was always just a temporary custodian of this marvellous institution. I am also of the view that all businesses need to refresh themselves with new management and ideas and after ten years in charge I believe it is appropriate for someone new to pick up the baton. I'm delighted Ed has accepted the role."
Gill was criticised by some United supporters after the Glazer family bought the club in 2005.
Co-chairman Joel Glazer said: "He is someone that has a reputation for decency and integrity and a man that has engendered the loyalty and total commitment of staff. He has been an invaluable confidant and adviser in the last eight years.
"David has played a significant role in the success of Manchester United in his ten years as chief executive and he can take great satisfaction in all that has been achieved on his watch, both on and off the field."