Former Arsenal defender Matthew Upson says the defence must be flawless tonight at Bayern Munich.
The Gunners are in Munich for the second-leg of their Champions League quarterfinal with the score locked at 2-2.
Upson told BBC Sport: "The margins are so small and it's funny that last week, we spoke before the game about how well they've been, really talking them up and that was probably the first game I've seen where they've made a little mistake.
"Since New Year, they've been rock solid and then again, just the pass out to Zinchenko on [Sunday] just little bits like that are costing them and in these matches, it just tips the balance.
"Tonight is total focus - no mistakes, no doubt. Be confident and hopefully that will get them out of that little rhythm of the last couple of matches where they've made just small mistakes but they've been costing them."
