The Premier League is of little importance to Arsenal for the rest of the season.The Gunners are languishing in sixth place and have no realistic hope of breaking into the top four, with Tottenham, Liverpool and Manchester United streets ahead of them.As such, domestic games have almost turned into a training ground routine for Arsenal, with all their focus clearly on the Europa League.Their second leg against CSKA Moscow - where they already hold a 4-1 win lead - clearly influenced Arsene Wenger's team selection against Southampton, with only four players keeping their place.And it was one of them who contributed heavily to the Saints' opening goal.Shkodran Mustafi was guilty of yet another ridiculous error, failing to deal with Dusan Tadic's cross and allowing Shane Long to sneak in and beat Petr Cech.It really was school-boy defending from a man who is the eighth most expensive defender in football history.

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As you can see from the footage, Mustafi is clearly the one in the wrong.

And Arsenal fans were not happy that the German international tried to pin the blame on his goalkeeper, despite the fact he had no realistic chance of getting to the ball in time.

The Czech custodian hasn't has his best campaign by any means, but he can't take the fall this time.

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Mustafi, take note.

The German defender has not been in Arsenal fans' good books ever since his disgraceful display v Manchester City in the Carabao Cup final.

His error for Sergio Aguero's goal that day hurt and despite a small return to form in recent weeks, it's clear the Gunners need an upgrade in the summer.