Manchester United manager Louis van Gaal admits he has been left with difficult questions to answer over the international break after his side were taken apart by Arsenal at the Emirates Stadium.

The Red Devils started the weekend top of the Barclays Premier League, but were usurped first by free-scoring Manchester City on Saturday and then the Gunners following an embarrassing 3-0 defeat on Sunday, with the hosts scoring twice within as many minutes early in the match.

An air of positivity had been building around Old Trafford on the back of four straight wins in all competitions, but Van Gaal was left as perplexed as he was angry by the manner of United's capitulation.

Arsenal tore United apart with two early goals in the space of 74 seconds, a backheel from Alexis Sanchez and a cool finish by Mesut Ozil, with Sanchez cracking home a superb third to put the game to bed after only 20 minutes.

United improved in the second half, but it was too little too late.

"We have lost in a way that you cannot lose when you are top of the league – you cannot start like we have started and the players know that," said Van Gaal, who had left defensive midfielder Morgan Schneiderlin on the bench.

"The worst thing is that everybody is going away, even out of London airports. They are flying away (on international duty) and I cannot build up a new situation that they have the confidence to play football, to win your next battle against Everton away."

Van Gaal was at a loss to explain the reasons behind the shambolic defensive display.

"I didn't expect that," he said. "I was surprised, amazed, maybe that is a better word – not performing our game plan, not the will to win. I didn't see that.

"When you give a team like Arsenal so much space to play football, then you know that you shall lose.

"And we have prepared ourselves also in that way, to play more contact, but don't lose your aggression.

"It was amazing for me and I am very disappointed."

Arsenal had come into Sunday's encounter on the back of a disappointing home Champions League defeat to Olympiacos and with the spotlight firmly back on manager Arsene Wenger.

The Gunners boss, however, paid tribute to the response from his players, with Theo Walcott again outstanding in leading a marauding frontline o the counter attack.

"It gives us a strong answer to all the questions raised in the week," said Wenger.

"To win in a big game is always a statement.

"We are in it, we are two points off the league leaders, Manchester City, so I hope that result will give us belief to fight for it."

Arsenal will be hoping Sanchez suffers no ill effects from the groin injury which forced him off during the closing stages.

Wenger said: "You cannot stop him from going to Chile and he loves so much to play for his country and he will play against Brazil (on Friday) and Peru (next) Tuesday, so the game at home against Brazil he will not want to miss. Hopefully he will come back in good shape."