Arsene Wenger admitted that he was "annoyed" after his 200th European game ended in a 3-1 defeat to Olympiakos.
Arsenal went into the match with the Group F top spot already won, but goals from Rafik Djebbou, David Fuster and Francois Modesto, along with a howler from replacement Gunners keeper Vito Mannone, left the French manager disappointed.
"I am annoyed," Wenger said. "It's difficult to single out [individuals]. We did not help our goalkeepers. We exposed them with the lack of quality and in the end they were quite brave.
"I feel offensively and defensively we were not convincing. We lost many challenges.
"You could feel there was more at stake for Olympiakos than us. I think that made us insecure defensively."
Olympiakos failed to reach the last 16 after Marseille defeated Borussia Dortmund 3-2 to secure second place in the group.
