Manchester United coach Phil Neville has warned the club that they must utilise the transfer window or run the risk of being "left behind".

The reigning Premier League champions have endured a mixed defense of their title thus far, with David Moyes's men sitting five points adrift of leaders Arsenal having amassed 20 points from their opening 11 fixtures.

Nevertheless, while Neville is adamant that the Red Devils still boast a capable squad, the former full-back has warned of the dangers involved in stagnation and believes recruits are essential.

"We have a fantastic squad as it is," Neville told 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]."

United travel to the Welsh capital for a clash with Cardiff City next Sunday on the back of victory, having beaten Arsenal 1-0 last weekend.