Arsenal manager Mikel Arteta expressed his disbelief at a disallowed goal during the 1-0 defeat to Leicester on Sunday.
Jamie Vardy came off the bench to score the winner for the Foxes in the 80th minute, but the Gunners felt they should have taken the lead earlier in the contest when Alexandre Lacazette headed in from a corner.
However, the goal was ruled out as Granit Xhaka was seemingly judged to have impeded goalkeeper Kasper Schmeichel while standing in an offside position.
"I’m really disappointed, we had it in our hands in the first half and I don’t know how the hell the goal was disallowed,” said Arteta.
"They caught us with space at the back and in that moment we lost the game. It is difficult to create spaces with 10 men behind the ball, but we should have finished the game better. When it comes to those moments you can’t give away chances at the back.
"We still had some moments after the goal but gave away too many free kicks. The effort that the boys put in, and the pressure the Leicester team put you under, it’s not an easy thing to do but we have to improve."
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The defeat is Arsenal’s third in the Premier League this season while Leicester move up to fourth.
"It is very difficult to create chances against 10 men behind the ball with no spaces,” said Arteta.
"We saw that they did that against Manchester City, and I was expecting them to do it. But we had an open situation where we should have finished the game better.
"Then it comes to two or three chances that you're going to have with set-pieces and when you have those moments, you have to make [something] of it and not make any mistakes at the back."