Manchester United boss Louis van Gaal has warned FA Cup opponents Arsenal never to count them out.

Van Gaal believes that spirit and refusal to accept lost causes - epitomised by Wayne Rooney's determination that led to the goal at Newcastle - can help steer them to an epic victory over Arsenal.

"We've shown a lot of times we have been coming back in the last minute, even when we are behind," said Van Gaal.

"At Newcastle we scored out of nothing because the ball was already lost, but because of Wayne's spirit he made it very difficult for his opponent.

"We've shown a fantastic fight and I'm very proud of our players."