Arsène Wenger admits that Roma's comeback against Barcelona last night was a 'warning' for him and his team in a pre-match press conference.
Roma beat Barcelona 3-0 and went through on away goals after the tie ended 4-4 on aggregate.
Barcelona let a three-goal cushion slip, and Wenger doesn't want this to happen to his Arsenal side as they look to guard against complacency against CSKA Moscow.
The Russian side were comfortably dispatched by Arsenal as they ran out 3-1 winners in north London, thanks to a Lacazette brace and a stunning Aaron Ramsey chip.
Arsenal travel to Moscow for the second leg of the tie, trying to not let their lead slip against their Russian counterparts.
However, as we saw in Rome, an away goal can be crucial, and that's what CSKA Moscow have.
Arsenal's only hope of silverware and Champions League football is through the Europa League. The Gunners main priority is the Europa League, and we've seen this as their performances recently in the league have been far different to the ones in the Europa League.
Wenger will need his side to not be complacent otherwise their comfortable lead could be snatched away from them by CSKA Moscow.
Another season without Champions League football will bring Arsène Wenger under more fire from Arsenal fans, and Wenger will make sure his team is well prepared for the task at hand.