Arsene Wenger said Arsenal “had got the job done” by advancing to the Europa League knockout stage as Group H winners despite losing away to Cologne.
A penalty by Sehrou Guirassy, after Mathieu Debuchy had harshly been adjudged to have fouled the French striker, earned Cologne only their second win in 17 Bundesliga and Europa League games this season.
The closest the Gunners came to scoring was when Francis Coquelin hit the post when the game was goalless in the first half.
With one match remaining, Arsenal have 10 points from five games, four ahead of Cologne and Red Star Belgrade, who were held to a goalless draw by Bate Borisov.
“You feel like you’ve got the job done when you finish top of the group,” said Wenger, whose side host Borisov in their final group game on 7 December.
“There’s nothing riding on that game, but we want to win it.”
A second successive Europa League win for Cologne means they could qualify for the knockout stage after losing their first three matches.
Of the five defeats Arsene Wenger’s side have endured this season, this was the least damaging after qualifying for the last-16 stage with two games to spare.
Yet a much-changed Gunners line-up failed to build on the afterglow of victory over neighbours Tottenham on Saturday as they suffered another loss in Germany.
They were hammered 5-1 by Bayern Munich in the Champions League in February 2017 and November 2015, as well as losing 2-0 to Borussia Dortmund in September 2014.
Wenger changed the entire starting XI from the north London derby, forward Danny Welbeck returning from a groin injury after missing the past seven games.
Arsenal’s side, which featured Olivier Giroud and Jack Wilshere, had only 16 Premier League starts between them this season and it was a lacklustre performance against the Bundesliga’s bottom club.
Coquelin twice went close to scoring his first goal for four years, the French midfielder fizzing a shot narrowly wide from 20 yards before another effort bounced off the foot of the Cologne post.
Welbeck lasted 45 minutes before he was replaced at the start of the second half by Alex Iwobi.
“Medically, the risk was too great to play him for longer than that,” added Wenger. “He was ready to stay on and frustrated to come off, but he’s in good shape.
“Welbeck, Giroud and Wilshere all looked dangerous, but we were lacking the accuracy and finishing.”
One of the few positives for Arsenal was another eye-catching display by 17-year-old Reiss Nelson.
The youngster has impressed in the Europa League and Carabao Cup this season, and he again caught the eye after replacing Calum Chambers midway through the second half.
In one sublime move, Nelson danced his way around three defenders before forcing a save from Timo Horn, who also stopped a long distance effort by Wilshere in the closing stages.