The 36-year-old admits David Moyes has a fantastic squad but highlights Manchester City's failure to strengthen in the summer of 2012 as the reason why they lost the titleManchester United coach Phil Neville admits the club will be in danger of being ‘left behind’ if they fail to bolster the squad with new signings.
United will make a fresh bid for Everton left-back Leighton Baines in January, although David Moyes has publicly played down expectations of securing a high-profile signing in the upcoming transfer window.
"We have a fantastic squad as it is,” Neville told the BBC's 'Football Focus'.
“In the transfer window early on in the season we were looking for players, that was well documented.
"That search continues. We need to keep reinvesting in the squad because if you stand still in this league you get left behind, as Manchester City found out last season when they didn't strengthen as much and they ended up losing the league [title]."
Neville has praised Wayne Rooney’s performances this season and says the England international, paired alongside Robin van Persie, will keep United in the title race this term.
"His level of performance not just in games but in training has been first class," Neville said.
"And at the start of the season when we weren't in the best of form, he was a shining light.
"Now you are seeing everybody else to come into form, and with the partnership between him and Robin van Persie, if they continue at that rate in terms of goals, then we will be right up there.
"If you look at facts, when they play together, Manchester United win football games."
Defeat at home to West Brom in September meant United suffered their worst start in the league for 24 years but four wins and a draw since the loss has put Manchester United five points behind leaders Arsenal.
Neville believes the players are now are buying into Moyes' playing style and concedes the club inevitably faced a sharp change from Sir Alex Ferguson's reign.
"Defeat by West Brom was a real wake-up call for the players and manager," he said.
"The players are beginning to trust the manager and his philosophy and I think you saw that against Arsenal."
"It was always going to take a bit of time after one man had controlled the club for so long, there was always going to be a transition period."