Despite a 5-0 aggregate victory against Fenerbahce in the same fixture last season, Wenger believes that the Gunners face a tough task overcoming Slaven Bilic's side.
He told reporters: "I believe it will be a very tough game and a very important one for us. We want to be in the Champions League group stage.
"Besiktas had a convincing result against Feyenoord, and so for us we have the luck to play the first game away. We know what is at stake of course and want to be highly focused for this
The winner of the tie stands to earn £7m in qualifying for the competition.