Laurent Koscielny out with back problem, Per Mertesacker ill

Arsenal's two first-choice centre-backs Laurent Koscielny and Per Mertesacker are both unavailable for tonight's Premier League match against Liverpool.

A back problem has seen Koscielny miss out on a place in the team, while an unspecified illness means that Mertesacker is also unavailable.

As a result, Calum Chambers and Gabriel Paulista have been selected at the heart of the Arsenal defence.

Further forward, Arsenal forward Olivier Giroud will make his 100th Premier League appearance, but Theo Walcott and Alex Oxlade-Chamberlain remain on the bench for the Gunners.