Per Mertesacker admits Arsenal “lost by far” against Napoli and “were always on the back foot.”
The Gunners were beaten 2-0 at the Stadio San Paolo and scraped through in second place thanks to a single goal in the head-to-head record.
Arsenal, Borussia Dortmund and Napoli all finished top on 12 points, but Rafa Benitez’s men still went out of the Champions League.
“It's a strange atmosphere at the moment because we lost, by far, especially in the second half,” defender Mertesacker told Sky Sports.
“We were always on the back foot. We took a little break today, but we'll be back on Saturday.”
Napoli would have knocked Arsenal out had they won 3-0, while only a late Borussia Dortmund winner against Olympique Marseille allowed the Germans to stay in the competition.
“We gave 10 per cent less mentally because we were always thinking we were through. I think we were lucky today but we deserved to go through because we played a good group stage. Now we concentrate.
“We're second in the group for the draw next week.”