Thinking that Madrid will be able to come back is like Thinking that Arsenal will not be playing in this game, I know anything is really possible in football but there are situations that when you look at critically and consider that which is involved you just understand and conclude that certain things are very likely not to happen such as this, Really Madrid need 4 goals to have a proper comeback enough to get them knocking Arsenal out and they need all four goals in one match but again Arsenal has got a better defence than Madrid does so I'm wondering how the magic will be done except if Arsenal gets to suffer red cards or have their key player injured which is almost not happening so it's an almost not possible task for Madrid but let's see, I will never say never because it's not over until it's actually over.
Real Madrid need to finish next quarter final with 3-0 scoreline to take the game to penalty shootouts. If Arsenal score one goal then Real Madrid has to score four goals to take the game to penalty shootouts. If Real Madrid directly want to qualify for semi finals without penalty shootouts then have to finish the scoreline 4-0. I don't think Arsenal will play that bad in next quarter final after giving there best in first leg. From my point of view, it will be worthy to place money on Arsenal for next leg then on Real Madrid.
And you can't call it a bad arsenal game. Arsenal can play as well as they want, but Real can just be better, at the expense of which they can win. Honestly the odds are pretty slim considering Arsenal can still score, which they probably will, but those odds are never zero. Real are a big and strong team, they can do anything, because they are pros in this tournament