David Beckham, former Manchester United winger
"As I have said many times before the boss wasn't just the greatest and best manager I ever played under he was also a father figure to me from the moment I arrived at the club at the age of 11 until the day I left."
David Gill, Manchester United chief executive
"We knew that his retirement would come one day and we both have been planning for it by ensuring the quality of the squad and club structures are in first-class condition. What he has done for this club and for the game in general will never be forgotten. It has been the greatest experience of my working life being alongside Alex and a great honour to be able to call him a friend."
Joel Glazer, Manchester United co-owner
"Alex has proven time and time again what a fantastic manager he is but he's also a wonderful person. His determination to succeed and dedication to the club have been truly remarkable. I will always cherish the wonderful memories he has given us, like that magical night in Moscow [2008 Champions League final win]."
Sepp Blatter, Fifa president
"His achievements in the game place him without doubt as one of the greats. Was [an] honour to present Sir Alex with award at 2011 Ballon D'Or. Will his longevity at the top ever be repeated?"
Gordon Taylor, chairman of the Professional Footballers' Association
The game of football will be a lot poorer place without him. He has been quite simply the best. He followed in Sir Matt Busby's footsteps and even surpassed him. He will be also be the toughest act to follow. I will miss him – he has been a very good friend of the PFA throughout his career. Of course at times it has not always been smooth and we have had a difference of opinion but we always respected each other and we have had a lot more agreements than disagreements."
David Bernstein, chairman of the English Football Association
"Sir Alex Ferguson's achievements are truly remarkable – he is genuinely one of the greatest managers of all time and certainly of the modern era. His contribution to English football has been outstanding in every regard and, in The FA's 150th year, it is something that should be celebrated. On behalf of The FA I'd like to wish him a happy and healthy retirement."
Paul Ince, former Manchester United player
"The man was immense. I'm totally shocked. What's he's done is unbelievable. You'll never see anyone of his kind again. Two weeks ago he was talking about staying on for another two years, so it's a massive, massive shock. The way he treated me was like a son."
Dwight Yorke, former Manchester United player
"He took the footballing world by surprise in retiring. With his hip replacement, and with David Gill going as well, that probably pushed him a bit into thinking he was going to retire. He wanted to regain the Premiership this year; he's done it, In many respects it's probably the right time to go. It will take some getting used to."
Sean Bones, vice-chairman of Manchester United Supporters' Trust
"We are all shocked...he's irreplaceable and he could continue for another five years but he deserves some retirement."
Clayton Blackmore, former Manchester United player
"It comes with a heavy heart. We have heard the rumours and the papers speculating, and I didn't want to believe it as he has done such a fantastic job and we wanted to keep him there. He deserves his time to sit back and enjoy what he has done. It is going to be emotional on Sunday. I'm sure the manager knows who will replace him and he will have his say. It would not surprise me if David Moyes takes over."
Vincent Kompany, Manchester City captain
"Sir Alex, one of the best managers of all time. After 26 years of success in the game, we all owe him a tribute."
Michael Owen, former Manchester United striker
"It's just not sinking in! Manchester United with no Sir Alex just doesn't feel right. What a man and great that it has ended on his terms...his record will surely never be eclipsed. He and the squad had planned to go to Chester Races today. Surely there will be a U-turn? Could be the biggest media circus ever if not!"
Peter Schmeichel, former Manchester United goalkeeper
"I can't make sense of the timing. It has come as an absolute bombshell. I'm disappointed and shocked."
Dennis Irwin, former Manchester United player
"It's a sad day for Manchester United. It's a day we should celebrate what he's done for Manchester United. It was always going to come as a shock. Without doubt the best manager that's ever lived."
David Gold, chairman of West Ham United
"Sir Alex, why are you retiring? I could understand it if you were old. Good luck in your future endeavours."
Rory McIlroy, golfer
"An end of an era today! Sir Alex Ferguson, the greatest of all time! United will have a tough time trying to replace him!"
Follow us @SprtNationalUAE