Van der Sar celebrated his 39th birthday on Thursday and Ferguson believes there is a more to come from the Dutchman.
"We are lucky to have such a great goalkeeper in the tradition of Peter Schmeichel, " he told United Review.
"I have always rated Schmeichel as the best goalkeeper in the world but I think now Edwin is right up there with him. I cannot separate them in terms of who is better.
"Edwin is such a great example of what can be achieved and how long you can last in the game if you keep the light of enthusiasm and ambition inside you.
"He is one of those players who has lived his life the right way. He celebrated his 39th birthday a couple of days ago and is as good as ever.
"How much longer can he carry on ? That is up to Edwin. He has earned the right to decide for himself without any pressure or persuasion for me. We will leave it up to him."