West Ham United manager Sam Allardyce has paid tribute to retiring Manchester United boss Sir Alex Ferguson.

The pair have built up a friendship over the years and Allardyce admitted to being shocked by the news.

Allardyce told the club website: "Sir Alex has had an unbelievable career, not just at Manchester United, but when he first started [at Aberdeen in Scotland]. For me, he is the greatest club manager that has ever been produced, certainly in this country, if not Europe.

"However many managers there were before him, the huge task he had was to achieve what Sir Matt Busby had done before him. For him to have done that and more, to have won the treble for Manchester United, and the joy and satisfaction of doing that was fantastic.

"To build as many teams as he has built over the seasons, on and off the field, was brilliant. He changed the backroom staff to support what he was trying to do and as a man, he is a fantastic human being.

"We will all sadly miss him, many others will too. Manchester United now have a massive task to replace him."