Arsenal's defence is proving to be a real problem for Unai Emery.

Heading into Sunday's trip to Premier League minnows Cardiff City the Gunners had conceded in each of their opening three games, six altogether.

And they once again failed to keep a clean sheet at the Cardiff City Stadium, conceding a sloppy goal to Victor Camarasa just before half-time.

Joe Bennett's cross somehow wormed its way to Camarasa at the back post, who leathered the ball past Petr Cech to make it 1-1.

Emery has Arsenal's defence trying to play out from the back but it's clear that they, alongside Cech, just don't feel comfortable doing so.

One player who did have a reasonably solid game at the heart of Arsenal's back four, though, was goalscorer Shkodran Mustafi.

The Germany international broke the deadlock in the 11th minute with a powerful header from Granit Xhaka's corner.

MUSTAFI SPARKS CONTROVERSY

Arsenal's lead didn't last too long but there's been a lot of talk on social media about the way Mustafi celebrated his goal.

In the video below, Mustafi finds the back of the net and goes to celebrate with Xhaka using the controversial Albanian double-headed eagle symbol.

So what's the problem?

Xhaka and Xherdan Shaqiri both performed the same celebration at the World Cup and were handed hefty fines. FIFA could have banned them if they wished to.

So there's a chance Mustafi, who was born to an Albanian family from Macedonia, could be fined or banned due to the political backstory of the double-headed eagle.

The Premier League and FA have the power to punish players for political acts, which would only make things worse for Arsenal. Here's how football fans reacted to Mustafi's celebration.