Right-back: Hector Bellerin
Bellerin was urged by Mesut Ozil to time his passes better against Palace and the little altercation made the news on the social media. As the first choice right-back, there are higher expectations of him. With his quick burst of pace, the Spaniard can support the attack when given the time and space. Against CSKA Moscow, Arsenal will have to be mindful of their counter-attacks and Bellerin must be wary of the opposition wingers.
Centre-back: Laurent Koscielny
Missing majority of Arsenal's previous Europa League match, Koscielny is set to be fit to start against CSKA Moscow. He was given a rest when his team played against Crystal Palace but the Frenchman is expected to play in the Europea League.
Centre-back: Shkodran Mustafi
The German was awful with his passing but brilliant with his interceptions and blocks. He played a crucial role of helping his team keep a clean sheet against Stoke City. Mustafi will certainly be playing once again in the backline.
Left-back: Nacho Monreal
Unless Monreal suffers an injury or falls ill, he is certainly going to start at left-back. His experience has been highly valued by Wenger who opts to play him in a back-four than switching to a back-three. The left-back can do better in linking up the play and moving forward. Apart from that, there are not many errors one can find regarding his defending.