Edwin van der Sar believes fans should be patient with David Moyes and the dip in form was expected.
The former goalkeeper appeared 186 times in his spell at Manchester United after signed from Fulham in June 2005 for a reported fee of £2 million.
Moyes replaced Sir Alex Ferguson this summer, but has been the subject of criticism for his side's defeats at the hands of Liverpool, Manchester City and West Brom.
The Red Devils are currently ninth in the Premier League and welcome Southampton, who have the league's best defensive record, to Old Trafford after the international break.
Van der Sar's last game for United was a 3-1 defeat at the hands of Barcelona in the 2011 UEFA Champions League Final.
The Dutchman told talkSPORT: "I think they expected that [the dip in form] because Sir Alex Ferguson was there for 26 years and the backroom staff left too.
"The players are still the same but you need to make adjustments to the style of play. 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."
The goalkeeper enjoyed six successful years at Old Trafford winning the Champions League and claiming four Premier League winners medals.
Despite the poor form showed by United, Van der Sar insists they remain title contenders and can pose a threat in Europe.
"Of course they are realistic contenders because they have great players with a lot of experience," said the 42-year-old.
"They have a lot of young players coming through because United are a team that give young players a chance. Maybe a little later than clubs like Ajax, but there is always a chance for the likes of Danny Welbeck, Jonny Evans, Rafael."
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