The Red Devils head into the new season following a disastrous spell under David Moyes last term as a seventh-placed finish in the Premier League resulted in no Champions League football for the first time since 1995.
"I think, after where we finished last season, [Van Gaal] needs to bring and create that winning mentality. That's huge," Ferdinand told BT Sport.
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Ferdinand, who joined QPR after ending his 12-year stint at Old Trafford this summer, admits that he and his team-mates struggled to deal with their poor form during Moyes's 10 months in charge.
"At a club like United, when you're within that bubble, when you lose a game, it's like the worst thing in the world and that's how it feels," the veteran explained.
"When you win, everyone goes crazy but the players keep a lid on it and think 'next game, next game, next trophy' but, when you lose, the downs are huge and so we never got out of that rut, it seems.
"But he's got to create that winning mentality. Bring a confidence back to the squad after finishing seventh because it's embarrassing. You're playing there and you finish seventh, you don't want to go to the shops, you don't want to walk on the street, see anybody.
"But he's got to start rebuilding all of that and it seems, after speaking to the lads who have been training there now, the confidence seems high."
United do not face a side who finished in the top four last season until they meet Chelsea on October 26 and Ferdinand maintains that a strong opening to the campaign is needed from the new manager.
"They need to get off to a winning start," remarked the 35-year-old. "I think it will set the tone perfectly for the season. Confidence will go through the roof and once Manchester United get that confidence going it's a hard juggernaut to stop."