Manchester United need to sign 'four or five players' to have any chance of winning the Premier League, according to Gary Neville.
Jose Mourinho has targeted four signings this summer and has already spent £105.7m on Everton striker Romelu Lukaku and Benfica defender Victor Lindelof.
The Portuguese also wants a defensive midfielder and winger, with executive vice-chairman Ed Woodward working on deals for Inter Milan's Ivan Perisic and Chelsea's Nemanja Matic.
And, with United's title rivals also strengthening this summer, Neville feels Mourinho needs at least the four names he wanted to improve on last season's sixth-place finish.
"United need to strengthen, but they all do - quite a bit," he told Sky Sports.
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"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."
United's bitter rivals, Manchester City, have already spent £122.5m on Bernardo Silva, Ederson and Kyle Walker while champions Chelsea have shelled out £69m on Antonio Rudiger and Tiemoue Bakayoko.
And Neville feels the Manchester clubs' aggressive transfer strategies could ultimately give them the edge in the title race.
"I said last season that the title would come to Manchester - and I was wrong - but I think this year it will," he added.
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"I think Chelsea will dip a little bit. Not in a negative way, but just having the Champions League will bring different challenges. I think Tottenham will be strong, but I feel that either United or City will win it, but I'm not sure who!
"I say it every year, whoever recruits best, wins the league. Chelsea getting N'Golo Kante was a masterstroke and Eden Hazard and Diego Costa came back to form. All the clubs are going for the same players, they're all expensive and controlled by agents.
"So, whoever has the best relationship, the best contacts and is willing to put the money in will probably do it."
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