HARD TASK:The Gunners face Milan tonightToday Arsenal    vs AC Milan SS3 21:45Benfica    vs ZenitON the face of it, Arsenal faces an insurmountable challenge against AC Milan on tonight, when they aim to overturn a 4-0 deficit in the second leg of the last 16 Champions League tie.After the crushing defeat in San Siro, Gunners boss Arsene Wenger said: "There is maybe a 2% or 5% chance statistically, but realistically we are out of this competition.”Milan coach Massimiliano Allegri remains cautious. "I wish to underline that we have not qualified yet,” he said.So do Arsenal have any hope of completing what would be the biggest comeback in European Cup history?"I’ve learned as a player and as an analyst not to ever rule anything out,” said former Arsenal full-back and BBC Sport pundit Lee Dixon. «But I feel Milan have enough about them to score."If they do, that will obviously be the end of the tie, so the all-important clean sheet and a good start defensively is key to the game. Yes, Arsenal need goals but if they go gung-ho early on and Milan score, it is all over.»There are instances in recent and not so recent European history of teams succeeding when the odds have been stacked against them.Milan and Zenit are the only teams in action this week who currently top their respective domestic leagues.Only three teams have ever overturned four-goal deficits in European competition and Arsenal coach Arsene Wenger effectively conceded the tie after the first leg at San Siro.