Sir Alex Ferguson insists Manchester United's Premier League title defence could yet unravel.

United occupy a seemingly unassailable position at the summit, with nearest rivals Chelsea trailing by five points with four matches remaining.

A 1-1 draw with Wigan saw the Blues lose further ground on Monday but Ferguson, speaking at the presentation of a Nationwide Lifetime Achievement Award to Denis Law, remains cautious.

"Wigan holding Chelsea puts us in a good position but in my experience in life you don't take things for granted," he said.

"We've got some difficult games ahead - Blackburn, West Ham, Chelsea and Wigan. We have three away games and one at home so we have to do a job.

"Because we have difficult games left, there is still a lot to play for and it could still go down to the wire.

"We could lose to Chelsea and we could lose all our remaining games. It's a very difficult league these days."