Manchester United manager Louis van Gaal has conceded that his side would find it "very difficult" to qualify for the knockout stages of the Champions League if they were to lose to Wolfsburg tomorrow evening.

The Red Devils were defeated 2-1 by PSV Eindhoven on matchday one to leave them bottom of Group B.

Ahead of the Bundesliga outfit's visit to Old Trafford, Van Gaal has claimed that a second failure on the bounce could prove costly to United's chances of reaching the last 16.

"In the Champions League you need to win all your home matches, otherwise it shall be very difficult [to qualify]. It's still possible, but very difficult. It's important that we win," the Dutchman told reporters.

When United played host to Wolfsburg in 2009 they ran out 2-1 winners thanks to goals from Ryan Giggs and Michael Carrick, the latter of whom has been ruled out of Wednesday's game through injury.