Per Mertesacker has revealed that he has never played as part of a back three in an alarming admission ahead of the FA Cup final against Chelsea.

The German made his first appearance of the season for Arsenal when he came off the bench against Everton in the final league game. Recovery from a knee injury killed his season but he could get a start at Wembley if Shkodran Mustafi is unable to shake off the concussion he picked up against Sunderland.

“I have never played in a back three, honestly,” Per said. “When I was young I started in a back four and that was my position from then on for the last 15 years.

“Everyone starts from zero with that new system. It means small adjustments but what it comes down to is knowing what the others are doing and giving them information that they know what you’re doing. Communication is the key in that system, even more.

“We feel more compact even in the middle and accepting sometimes ‘Just defend, just defend’. We’re getting the ball sometimes so just allow ourselves to relax a little bit more.

“With a back four we felt we have to get the ball, we have to play, we have to press, especially against Manchester City (in the semi-final, which the Gunners won 2-1); we allowed ourselves just to defend from the box, not even open up too much.

“It’s still a learning curve though for us, the back three, and for those who haven’t played that system this season.

“We had to change to a back four against Everton due to that red card, but what made the difference against Everton was the communication, especially against each other. That’s what we need to do on Saturday.”

Nacho Monreal is expected to start as a centreback with the Ox ahead of him on the left and Hector Bellerin ahead of Rob Holding on the other side.

The place in the middle will be taken by either Mustafi or Mertesacker with Wenger set to make a late decision on the younger German after he missed training again on Friday.

David Ospina will start with Petr Cech dropped. Initially thought to be injured, the Czech is said to be ‘devastated’ at missing out and will be on the bench for the game against his former side.