The Gunners came into the second leg of their last-16 tie against Sporting with the game finely poised at 2-2.
Granit Xhaka gave the hosts a first-half lead, before Sporting equalized thanks to a long-range stunner from Pedro Goncalves.
The game eventually went to penalties where Gabriel Martinelli missed his spot-kick and the visitors won 5-3 to progress to the quarter-final.
“A huge blow obviously. There were moments in the first 75 minutes where we weren’t at our level. We gave every ball away and we didn’t have the capacity to take the game. There were chances to win it in extra-time. There was a lot of uncertainty with the pens.
“We didn’t win enough duals in certain spaces. We didn’t put the ball under pressure well enough. We gave the ball away consistently and it created a really open game we didn’t want to play,” Arteta told BT Sport.
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"We weren't at our level." 😤
— Football on TNT Sports (@footballontnt) March 16, 2023