Van der Sar is convinced Van Persie will shoot United to the Double.
He said: "I had the chance to catch up with Robin last week in Holland.
"We talked about life in Manchester and it is obvious he thinks it's fantastic. And why not when you are top scorer of a team which is on course to grab the Premier League title?
"Robin has been performing brilliantly for three years non-stop. But when you are top of the league, your performances are more in the limelight.
"He is fully in control and relaxed, showing confidence on and off the pitch. That confidence, linked to his real class and quality, gives him that extra value for the team."