Arsenal boss Mikel Arteta explained fielding Declan Rice at centre-half for their 1-1 draw with PSV.
Rice dropped back from his usual midfield role for Arsenal's final Champions League group game.
Arteta explained: "We are very short at the back and I really wanted to try if something happens, how we're going to resolve that situation. I thought he was really good.
"He has played there before. We have to try as if we have an emergency we have to understand and to be sure that we can fill that gap in the right way. He has a lot of composure on the ball, he wins a lot of duels for a player of his size and he has done it in the past.
"He is a good option."