And Leno has warned his team-mates that they cannot afford to play that poorly again if they are to achieve their aim of winning the Europa League and qualifying for the Champions League.
“We need to be 100 per cent every game,” he said. “If we play like today then we won’t reach anything this season.
“I think we suffered today and it was not necessary. I think because in the first 15 or 20 minutes we controlled the game, but then we’ve made too many easy mistakes and in the second-half we conceded the goal and then everybody was nervous.
“We made it hard for ourselves and, like I said, it was not necessary. In the dressing room it was quiet because everybody knows that it was not a good performance from us. We cannot change it anymore but the positive thing is that it was a warning.”
Given Arsenal’s lead from the first leg, an Olympiacos upset always looked like a tall order – even after their heroics last season.
However, when Youssef El-Arabi struck in the 51st minute, there was a glimmer of hope for the Greek side.
Arsenal ultimately saw the game out, but it was not the controlled performance Arteta wanted and he is well aware this type of display cannot be recreated in the quarter-finals.
“If we want to have any chance in the competition, we have to do things better than that,” he said. “It was a difficult opponent in this round. Benfica was a really difficult opponent as well. They’re all going to be.
“The level is really high in the Europa League at the moment. It’s not like 10 years ago I think. I think the level is much higher.”
Given the fact Arsenal are 10th in the Premier League, winning the Europa League is their best route back into the Champions League and there is no margin for error.
“I think there are only very good teams in the quarter-finals and we need two perfect games to go to the semi-finals and two more games to go to the final. This is our target,” said Leno.
“The Europa League is very important for us. This is probably the closest way to go to the Champions League and also to win a big European trophy so we need to step up.
“We need to have the motivation to win every game, cut out the easy mistakes and go through to the final and hopefully have a big final at the end of the season.”