The Red Devils signed three players in the summer transfer window to improve Mourinho’s squad but Manchester United missed out on a couple of big name signings.
Manchester United signed Shakhtar Donetsk midfielder Fred, FC Porto teenager Diogo Dalot and Stoke City goalkeeper Lee Grant in the summer transfer window.
However, Mourinho missed out on a new centre-half despite being linked with a swoop to sign Leicester defender Harry Maguire, Spurs centre-half Toby Alderweireld and FC Barcelona’s Yerry Mina.
Manchester United were unable to get a deal over the line for a winger, too, although Inter Milan’s Ivan Perisic, Chelsea FC star Willian and Real Madrid star Gareth Bale.
The Red Devils lost 3-2 to Brighton and Hove Albion in the Premier League on Sunday to slump to their first loss.
Former Manchester United defender Neville believes Mourinho needs more backing in the transfer window.
“Manchester United have had a problem since Sir Alex Ferguson retired in the transfer market with David Moyes and then Louis van Gaal You could argue £350m to £400m of the £700m that has been spent has not been wasted, but it’s not value for money,” Neville told Sky Sports.
He added: “He needs further investment. It’s obvious that he does and the club should support him in that because you can’t withdraw part way through a process. They have to go for it.”
Manchester United haven’t won the Premier League title since 2013 when Sir Alex Ferguson led the Red Devils to a 13th top-flight crown.
The 20-time English champions will face Tottenham Hotspur next Monday.
MORE: Man United latest news
MORE: Arsenal latest news
MORE: Chelsea latest news
MORE: Liverpool latest news