Arsenal manager Arsene Wenger admitted that his side had lost concentration during their 2-1 Champions League reverse away to Shakhtar Donetsk.
The Gunners took an early lead in the Donbass Arena through Theo Walcott, but were behind by half-time and failed to recover after the interval, leaving them still short of securing a place in the knockout stages.
Wenger told reporters:"Congratulations to Donetsk, they played well and won the game.
"We had a good start, but after that we lost our urgency and let Donetsk come into the game too much.
"We lost concentration in the duels and you could see what was coming towards half-time.
"I felt we moved out of the game altogether and moved into the game altogether, so it was more of a team problem, a kind of complacency problem more than an individual problem.
"In the second half we came back into the game and gave a lot, you cannot fault the team and we were a bit unlucky.
"We have learned the lesson that at this level you cannot lose focus at any moment and that is why we were punished. But we are still in a strong position in the group."