Mikel Arteta saw his Arsenal side reach the Europa League quarter-finals despite losing at home to 10-man Olympiakos 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.