The 39-year-old Dutchman's performances have been of their usual top quality, leading to the belief he will sign another one-year contract.
There are even rumours of a possible return to international football with Holland at next summer's World Cup - when he will be only four months short of his 40th birthday.
"I don't know his plans," said Sir Alex Ferguson.
"When you get to that age and have a young family, there are a lot of things to consider.
"It is usually sometime in December that he outlines his plans and how long he thinks he can go on.
"He is a very intelligent man, who understands his body better than anyone. He will come to the right decision."
Sir Alex is equally confident of the future when van der Sar bows out.
"I have said all along, Ben has terrific ability," the manager stated.
"He needs plenty of game experience, which he has not got at the moment, but the future rests with him and Tomasz.
"The two of them will fight it out, I am sure of that."
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Big Ben, Tock Tick (25/11/2009 at 12:19)
Still with no money in the pot I suppose he will have to do.