Former United goalkeeper Peter Schmeichel said he was "shocked" at the news of Ferguson's retirement.
Disappointed, shocked, sad. Didn't think THAT day would be today.
Sir Alex Ferguson's brisk way with words has influenced the way we talk about football.
A timeline of the life of outgoing Manchester United manager Sir Alex Ferguson.
A special photo gallery of Sir Alex Ferguson's career at Manchester United as he steps down from his post as manager of the club.