Manchester United have already splashed out just over £100m on Victor Lindelof and Romelu Lukaku.
But Jose Mourinho is intent on bringing in more fresh talent as he looks to build a squad capable of challenging on all fronts with Champions League football returning to Old Trafford next term.
A deal is thought to be edging closer for Inter Milan's Ivan Perisic, while Chelsea's Nemanja Matic and Tottenham midfielder Eric Dier both remain on Mourinho's radar.
But former Red Devil Neville believes all the teams at the top need to strengthen if they are to challenge for the Premier League title.
Gary Neville believes Manchester United need to bring in four or five players Premier League Done Deals: Every signing so far in the 2017 summer transfer window Thu, July 13, 2017
Express Sport brings you up to date with every new arrival in the Premier League during the 2017 summer transfer window
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Tiemoue Bakayoko – Chelsea (Undisclosed from Monaco)
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 need to strengthen, but they all do – quite a bit," he said.
"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.
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Jose Mourinho is keen to bring in a defensive midfielder
"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."