The Dutchman spent six years at Old Trafford, winning the Champions League and four Premier League titles, and believes his former manager's achievements are unsurpassable
After his arrival from Fulham in 2005, Van der Sar finally laid the goalkeeping demons that had haunted the club since the days of Peter Schmeichel to rest, spending six season at United.
During his career at Old Trafford, the former Netherlands international won four Premier League titles, the Champions League once and two Capital One Cups but Van der Sar insists it is the achievements of Sir Alex that will never be matched.
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“This will only ever happen once [at the club]. Someone with such an illustrious career as Ryan Giggs has never had another manager."
"Of course, he's reached a respectable age. What he has done for United is incredible. He left his mark on the club in 27 years and surrounded himself by his own people. Rene Meulensteen for example is very important as a coach.
The 42-year-old also revealed he had a conversation with the retiring United boss last week and had an inkling that he was about to hang up his boots.
He added: "He called last week and after that conversation I had a bit of that idea.
"I got to know him as a very warm man. You could discuss anything with him. He was once standing next to my goal to tell me that he was so proud of his grandson, who once performed at a Christmas concert with my son. In between, I had to perform a save and then he went on."