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.
What a privilege to have played under arguably the best manager the world has ever seen.
His record will surely never be eclipsed. Simply astonishing to read through his managerial record of achievements.
Thanks Gaffa for the chance you gave me back in 1992 to play for the BIGGEST club in the world & grace OT as a Man United player #indebted
Former Cambridge United and Norwich City star Dion Dublin has paid tribute to Sir Alex Ferguson.
Dublin was brought to Old Trafford by Sir Alex after scoring more than 50 goals for the Abbey Stadium outfit.
For more on this story head to ITV Sport.
Proud man. Great manager. Staunch Labour Party supporter. Sir Alex Ferguson will never be forgotten.
Joel Glazer, joint chairman of the Manchester United board with brother Avie, pinpointed the 2008 Champions League final penalty shootout success over Chelsea as a highlight among the many memories of Ferguson's time at the club.
He said: "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."
Avie Glazer added: "I am delighted to announce that Alex has agreed to stay with the club as a director.
"His contributions to Manchester United over the last 26 years have been extraordinary and, like all United fans, I want him to be a part of its future."
Former Manchester United footballers Danny Simpson and Ravel Morrison, who both played under Sir Alex Ferguson, tweeted their surprise and sadness that the manager is to retire:
Wow I can't believe Sir Alex has actually retired. It doesn't seem real. He's an absolute legend n I'm privileged to say I worked with him
sad new Alex ferguson will retire ????
Press Association chief football writer Simon Stone said no press conference was expected today from Sir Alex Ferguson.
Am told no press conference today.