Neville feels that the size of the task at United has caught Louis van Gaal by surprise, despite the club's struggles last season.
He told Sky Sports News: "At this moment in time this Man United team isn't good enough to win the league. Louis Van Gaal asked for three months when he came in and he's reassessed that. It's a tougher job than he imagined and in the next eight games they've got tough opponents.
"At the start of the season after eight games you would have said they would have been on 16 or 17 points. There's been a lot of upheaval. It's been tough for him. Coming out of the World Cup he was drunk with praise, but I think it's sobered him up slightly.
"There's a big belief, I think he will get it right. A lot of good players have been signed but there's been so many injuries, particularly in defence. There's something there but it's going to take him longer."
United face Chelsea in their next top-flight match at Old Trafford on Sunday.