The La Liga side could only muster a third-place finish in their Champions League group, which saw AS Roma and Chelsea advance to the knockout stages, dropped into the second-tier competition but were a seeded side for the draw so were always likely to get a favourable tie.
The Gunners will face Swedish debutants FK Ostersunds, who finished second in a tough group that also included Athletic Bilbao and Hertha Berlin, and should have no problem reaching the last 16.
Coming in at 9/1 (10.0) are Borussia Dortmund and Napoli, who were both handed tricky draws by UEFA; the Bundesliga side play Everton-conquerors Atalanta, whilst the Serie A outfit will have to overcome fellow Champions League dropouts RB Leipzig.
A pair of Italian sides are available at 12/1 (13.0) in Lazio and AC Milan. The former face Steaua Bucharest, meanwhile the Rossoneri will hope their season is back on track by February and that they can navigate past Ludogorets.
At 16/1 (17.0) are Villarreal, but a far more tempting shot is Lyon at 20/1 (21.0). These two sides play each other in one of the most mouth-watering ties of the round, but the latter are currently second in Ligue 1 behind runaway leaders Paris Saint-Germain and have the players to land a first major trophy since 2012.