The former Ajax and Juventus stopper retired from international duty with the Netherlands at the end of Euro 2008, although he returned on a one-off basis during October's World Cup qualifiers because of injuries.
Van der Sar's rivals for the United goalkeeper's jersey, Ben Foster and Tomasz Kuszczak, have so far failed to usurp him on a permanent basis.
"What he has done really well for us over the last couple of years is help to develop the younger goalkeepers," said Ferguson.
"We are using Ben and Tomasz quite a bit now, which allows us to freshen Edwin up for the really important games.
"Edwin has bought in to that very well. He understands the situation completely. He is playing a great part in ensuring the big picture is there for us with Ben and Tomasz."
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