Petr Cech has been a scapegoat at Arsenal over the last few years, make no mistake. He's not been at his best for a while, and whilst he has undoubtedly cost the Gunners points, it's fair to say that he's not the only problem at the Emirates. 

Indeed, replacing the goalkeeper is not the only thing that Unai Emery needs to do at Arsenal, nor is it the most pressing task at hand. Rather, major concerns still remain in the Arsenal defence, and one player that is sure to cost the Gunners points over the course of the season is Shkodran Mustafi.

Of course, you could point towards Arsenal's long 9-game winning streak as proof that the Gunners are on the right track, and whilst that's certainly been true of much of the team, there have been signs of concern at the back. Arsenal's defence has looked poor at points, and there have been more than a few games in which they've only been able to avoid conceding by the skin of their teeth.

Mustafi, in particular, has regularly been at fault. He's been far from faultless during his time at Arsenal, and it's fair to say that inconsistency has been a real problem at the club for a while now. On his day, he's as solid as a rock, but the German is far too often a problem at the back.

Mistimed tackles, a lack of concentration and rash decision-making, Mustafi is not yet a player that Emery can consistently rely upon.

It's no surprise that Arsenal conceded against top Premier League teams like Chelsea and Man City, and a good run against mid-level teams should not take away from the problems that are present in the Arsenal attack. Mustafi, in particular, is a real worry. The 2 errors leading to a goal that he made last season could grow even higher this year, at least judging by his early season performances.

Arsenal have a ready-made solution to the Cech problem in Bernd Leno, but they have no such replacement for Mustafi.