Mikel Arteta saw his Arsenal side reach the Europa League quarter-finals despite losing at home to 10-man Olympiacos before declaring they must improve in the next round or be knocked out.
The Gunners were beaten 1-0 at the Emirates Stadium as Youssef El-Arabi scored against Arsenal for the third game in a row.
Recalled skipper Pierre-Emerick Aubameyang missed a number of good chances to kill off the tie but a 3-1 win in Greece last week was enough to see Arteta's side through.
But the Spaniard warned his players they would not be going any deeper into the competition if they do not improve on their latest Europa League performance.
Asked if they will be out if they play as badly in the next round, Arteta said: "Yes, because what we have to do, the way we are set up, the organisation we have and the way we want to play, we have to be much more efficient, much more simple, much more cohesive as a team.
"Without that structure you are exposed when you lose the ball in really dangerous areas without any opposition.
"When you do that, and we did that as well where we created chance after chance, but again, we want to be in the competition, and when you have four, five, six big chances in Europe you have to put them away and then the tie is over."
Olympiacos made a good fist of overturning a two-goal deficit from the home leg, attacking Arsenal after half-time and catching them cold.
Onto the next round – together! ✊🔴 🏆 #UEL pic.twitter.com/Bav5rCEjR2 — Arsenal (@Arsenal) March 18, 2021
They never truly looked like causing a bigger upset, especially when defender Ousseynou Ba was sent off late on after picking up two quick bookings.
Arteta pointed to Tottenham's shock elimination to Dinamo Zagreb, their north London rivals losing 3-0 after extra time in Croatia, as an example that the Europa League is a more difficult tournament to win than it is given credit for.
"It shows as well the level of the opposition," he said of Tottenham's loss.
"People take for granted that you play against any opponent and you're going to be through because of the name of the club they represent.
"It's not like that. Every team in Europe is really difficult to beat."
While Arsenal advanced, their performance left plenty to be desired, especially when it came to drawing a blank in front of goal.
Aubameyang was the main culprit, the striker back in the starting line-up having been dropped for Sunday's win over Spurs due to a breach of pre-match protocol.
Arteta said ahead of the defeat to Olympiacos that he had held positive talks with his skipper and that the incident was now in the past.
"I hope it doesn't," he replied when asked if Aubameyang's profligacy could have been as a result of a hangover from the weekend's incident.
"We've moved on from that. He started the game today and we expect him when he does play that he performs at the level that he can."
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