Neville insists the Red Devils need far more quality if they are realistically going to battle for major silverware this season.
He told Sky Sports: "United need to strengthen, but they all do - quite a bit.
"Even the champions need to if they're to repeat what they did last season.
"You're not just talking about winning the Premier League title, you're talking about competing in Europe.
"English clubs have been well short in the last few seasons.
"All big clubs want to be winning Champions Leagues.
"That won't happen unless they significantly improve. United need to sign four or five players."