Former Manchester United defender Phil Neville believes this summer's big spending by the Red Devils will need to be repeated in future transfer windows before the club can again be seen as title contenders.

Last season's seventh-placed finish in the Barclays Premier League led new coach Louis van Gaal, appointed in place of David Moyes, to splash out over £150million on Angel di Maria, Luke Shaw, Ander Herrera, Marcos Rojo, Daley Blind and loan signing Radamel Falcao,.

Absent from that list, though, was an out-and-out central defender, a position which has seen United struggle this season as Chris Smalling, Phil Jones and Jonny Evans battle for form and fitness and youngster Tyler Blackett seeks to establish himself.

And Neville believes that is the biggest issue still to be addressed.

"I know United have spent £150m," he told BBC Radio 5 live.

"I think there's another two transfer windows of similar amounts of money needed – maybe £100m – before they can even think about winning the title.

"There are still key positions in the team that need filling. I think the centre-back position is obviously the key area. Holding midfield or centre midfield needs addressing too.

"There were no world-class centre-backs out there (this summer). I think that's why in the next two transfer windows, United might still be looking for that world-class defender."

However, he backed England internationals Jones and Smalling to eventually prove their worth to the club.

"I am certain Chris Smalling will come good and I have full faith in Phil Jones as well," he said. "They've bought of a lot of foreign players, you don't get rid of your English spine."