Arsene Wenger has accused Arsenal of failing to adhere to their game plan during the 2-1 Premier League defeat to Everton on Tuesday.
Headed goals from Seamus Coleman and Ashley Williams saw the home side come from behind at Goodison Park and inflict a first defeat since August upon the Gunners.
Wenger was frustrated at the way his side conceded and said the players were guilty of "not respecting the rules" that were laid down in the preparations for the match.
"We started well and were in control of the game," he told Arsenal Media. "After that, we lost a bit of urgency and Everton made the game very physical.
"From that moment on we lost some goals we are not used to losing. They disturbed our game, really, they played a real cup game and at the end of the day we lost from two headers from two defenders.
"You could expect [Romelu] Lukaku to score a goal against us but not the way we conceded two goals here.
"We knew exactly what was happening and the first goal is exactly what we planned not to do. We have to look at ourselves because we punished ourselves by not respecting completely the rules that we put out the night before we played."
The defeat means leaders Chelsea can move six points clear of Arsenal by beating Sunderland at the Stadium of Light on Wednesday.
The Gunners travel to Pep Guardiola's Manchester City in their next match.