The 19-year-old central defender is one of several players Arsene Wenger has been forced to deploy at left-back in recent weeks following the injuries to Andre Santos and Kieran Gibbs, but even without much defensive consistency, the Spaniard believes Arsenal will win if they stay focussed.
Speaking to Arsenal’s official website, the Barcelona native said: “We know that with the FA Cup it is only one game, so you can't make any mistakes.
“You have to make sure you are ready for anything that happens, but still go out there and try to win the game.
“We played them a month ago [in the league] and only scored the winner in the 87th minute, so it will be tough. We are at home, we have our supporters there but we know we will have to work for victory.
“They have a very good striker in Darren Bent and two quick wingers in Marc Albrighton and Charles N'Zogbia. They are dangerous and they can make things happen.
“We need to stay focused and make sure we don't make any mistakes at the back. If we do that then we have a big chance to win.”