Nigeria international and Arsenal midfielder, Alex Iwobi, picked up an injury as Arsenal were stunned 2-1 by Ostersunds at the Emirates Stadium in their UEFA Europa League return fixture on Thursday evening.
The London club are still through to the round of sixteen on 4-2 aggregate score.
Iwobi was replaced by Reiss Nelson in stoppage time while ex-Flying Eagles striker Alhaji Gero was a non-playing substitute for the Swedish club.
The Gunners won the first leg 3-0 but one of football’s great shocks looked possible at half-time after the visitors struck two goals in 70 seconds.
Graham Potter’s side, who have risen from Sweden’s fourth tier since 2010, were on top in the first half and led 2-0 thanks to Calum Chambers’ own goal – deflecting in Hosam Aiesh’s shot – and Ken Sema’s clinical strike.
But the Gunners – who named a reasonably strong side only three days before their Carabao Cup final with Manchester City – improved slightly after the break and Sead Kolasinac finished from Hector
Bellerin’s cross to relieve the sense of dread inside Emirates Stadium.
“We were not at the races in the first half,” said Wenger, who saw his side booed off at half-time and full-time.
“I think in the second half it was much better and we should have scored a few goals.
“In the first half we were in trouble and in danger because we were complacent, not focused and were open every time we lost the ball. We had no ideas with the ball and that’s why we were in trouble.
“We responded very well because we did the job to qualify, but that’s what we have to take from the night and that’s all.”
Arsenal, who have never won the Uefa Cup or Europa League, will discover their last-16 opponents at 12:00 GMT on Friday.
Ostersund are only the second team to win a game at the Emirates in the Gunners’ last 28 matches – a run dating back to March 2017.