Honestly, if Wenger were tactically flexible, this would be the time to go to 3 at the back:
Maitland-Niles/Jenkinson -- Monreal
The idea of Jenkinson starting in a back 4, without significant protection, against serious opposition, is very scary.
Anyways, what do you expect? You come in to the season with no other plan than to play Bellerín every fucking game, well this is what happens. Just as it happened to Cazorla and can happen to Özil and Sánchez in the future.
November is not some kind of anomaly or bad luck. It's 2 and a half months in the season and it's when muscle injuries start popping up systematically after a few good 3 games in 7 days weeks, and as Wenger now has gone years without planning the squad very well/being terribly reliant on a few players, you get the results you do when the injuries hit.