Arsene Wenger admits Arsenal were “nervous in the end” after scraping through despite a 2-0 defeat to Napoli.
The Gunners qualified behind Borussia Dortmund, though only on goal difference in head-to-head results as they all finished top of Group F with 12 points each.
“We are happy to be through because it was very difficult,” said Wenger. “We took it very seriously but in the second half we dropped physically a lot, we had a game on Sunday.
“Napoli played very well tonight but we were a little bit on edge for some minutes, it was nervous in the end, but we got through.
“The most difficult is when you are in between, do we attack or defend? As long as we didn't score, they had hope.
“Maybe what helped was that Dortmund were drawing 1-1 and maybe they put the handbrake on, that's why we didn't get too much pressure in the end.”
Arsenal went down to 10 men in the final stages for a second Mikel Arteta booking.
“He’s absolutely convinced that he didn't make a foul and it was very harsh but he already had a yellow card. It's always difficult in the middle of the park. I felt it was a very harsh second yellow card.”