Arsenal captain Mikel Arteta was left shell-shocked by their 3-3 draw with Champions League opponents Anderlecht.
The Gunners were 3-0 up on the night, but after a last-minute Aleksandar Mitrovic header, could only manage a 3-3 draw.
"Arteta was honest in his summary of the game: 'I don't know [how it got away from us]," he told Sky Sports after the final whistle. "We can't afford to make those mistakes, it's just not good enough.
"We had a 3-0 lead at home and we know what we're playing for. We'll analyse the mistakes and see what happened in the second half. It's not up to the level of this club.
"The main aim when you start the competition is to win the group but we have thrown everything away tonight. You can't do that in this competition."
