Van der Sar almost reversed retirement
The 40-year-old Dutchman takes part in his last Premier League match for United when the champions host Blackpool today, before playing the final game of his career in next weekend's UEFA Champions League final against Barcelona at Wembley.
Van der Sar has been in such good form this season that his United team-mates had been trying to persuade him to play on for one more year.
In his programme notes for the match against Blackpool, Ferguson wrote: "Edwin decided he wants to go out at the top, though he did have a wobble last week. He came to see me and told me he was thinking about changing his mind.
"I had to tell him to be quick about it because we are in the middle of concluding a deal for a new keeper. He came back a couple of days later to say he would be sticking with his original decision to go, which I think at his age is the right thing for him to do."