United sailed to the title last season under the guidance of Alex Ferguson, finishing 11 points clear of rivals Manchester City, but they appear to have gone backwards with David Moyes in charge.
The Scot, who assumed the reins from his long-serving compatriot in May, has seen his men win just three of their opening seven league games, with a shock home defeat to West Brom representing a low point in their campaign.
But Van der Sar, who kept 87 clean sheets in the 174 matches, urged fans to give Moyes time to get things right.
"The players are still the same but you need to make adjustments to the style of play," he told talkSPORT.
"They had a good win at Sunderland but of course, you don't expect to lose at West Brom at home, those were expensive points.
"Even last year they had a bad start but Robin van Persie, with all the goals scored, was on fire and hopefully this year they can do it again.
"Traditionally Man United never have a great start and at the moment the change of manager is quite difficult for them.
"They've had so much success over the years with Ferguson so it's normal to have a dip and even Ferguson did not win the league all the time.
"So there’s a chance you don't win anything in the first season or even the second season but hopefully there's faith in what he can do."
United, who are now unbeaten in their last two games, will hope to continue in the same vein when they host Southampton on October 19.
