Shkodran Mustafi injury poses big test for Arsenal defence
Just when Arsenal's defence was starting to look solid for once, Shkodran Mustafi's injury is set to pose a big test for the Gunners.
Mustafi limped off during Germany's World Cup qualifying win over Azerbaijan on Sunday, with Joachim Low saying he was set for an "extended layoff" with what looked like a severe muscle tear in his thigh.
Even a light muscle tear normally means about three weeks on the sidelines, meaning Mustafi could be out until the next international break at least. That's especially bad news given that Laurent Koscielny is also suffering from a flare-up of his chronic Achilles' tendon problem. Arsenal struggled badly without those two at the start of the season, but have since kept four straight clean sheets in the Premier League with Mustafi playing in the centre of a back three.
Arsene Wenger faces a difficult choice as he tries to make sure that Arsenal's infamously wobbly defence doesn't become vulnerable again.
Here's a look at his main options ...
Stick with a back three
If Koscielny is fit to return against Watford, the simplest choice would be to just replace Mustafi with either Per Mertesacker or Rob Holding while sticking with a back three formation. Mertesacker could take Mustafi's place in the centre of defence, allowing Koscielny to remain on the right side with Nacho Monreal on the left.
However, Wenger has been curiously reluctant to play Mertesacker in the league despite his fine showings in other competitions -- perhaps because of his lack of pace. If Wenger opts for Holding's athleticism rather than Mertesacker's experience, that would probably entail shifting Koscielny to the central position.
Revert to a back four
Despite Arsenal's defence looking decidedly more solid since Wenger switched formations late last season, you still get the feeling the Frenchman is aching to revert back to his more attack-happy 4-2-3-1. Mustafi's injury could be the perfect excuse.
By pulling Hector Bellerin and Sead Kolasinac back into full-back positions, Wenger could then fit in another attacking player in his lineup instead of an additional defender. He'd just have to decide whether Monreal, Mertesacker or Holding would make the best centre-back partner for Koscielny. With Mesut Ozil hopefully ready to return after a knee problem and Alex Iwobi showing good form before the break, this may be an enticing option for Wenger.
The back three is clearly a useful Plan B for big away games, but Arsenal's next four domestic opponents are Watford, struggling Everton, Norwich and Swansea. It seems like a perfect opportunity for Wenger to show off the full strength of his attack.
A front four of Alexis Sanchez, Ozil and Iwobi playing behind Alexandre Lacazette should score enough goals to make up for whatever wobbles may appear in defence. And it would leave Manchester City guessing as to which formation Wenger will use for his trip to the Etihad on Nov. 5.
Mattias is ESPN FC's Arsenal correspondent. Follow him on Twitter: @MattiasKaren.