The Gunners boss believes his side had to pay for their below-par defending after throwing away a 3-0 lead against Anderlecht on Tuesday night.
Arsenal looked to seal the three points of the clash as goals from Mikel Arteta, Alexis Sanchez and Oxlade-Chamberlain gave the home side a 3-0 lead.
However, Anthony Vanden Borre's goal in the 61st minute reduced the lead to 3-1 before netting a penalty and Aleksandar Mitrovic spoiled the Gunners party after he levelled to make it 3-3 in the dying minute of the Champions League clash.
Arsene Wenger's men could have qualified for the knockout stage with a win hoping to top the group but still need a point to seal a place in the last 16.
“I believe defensively as a performance across the pitch, we were very, very poor tonight,” said the Arsenal boss.
“You have to give them [Anderlecht] credit because the fought until the end and we had a poor defensive performance from the first to the last minute today.
“We never felt comfortable and somewhere we got punished because of bad luck. The first goal was offside but defensively our performance was not good enough to do it.”
Wenger continued: “Secondly at 3-0 we thought the job was done and it was a combination of switching off and fatigue as well.
“You could see we couldn't win the challenges and they finished stronger and sharper – we got punished.
“It’s very disappointing but overall over the two games we got four points. I think we are well paid for our two performances.”