All of our defenders?
We had the third (?) most solid defence last season. Koscielny is clearly up there with the best CB's in the business, and Mertesacker has been quality for a while now. Although he is prone to being caught on the break considering he's very slow, but his positioning and judgement cover his lack of acceleration and agility. Vermaelen has missed a lot of Football and has a lot of catching up to do. IF he can re-capture his first season form then we will have 3 strong options and a reliable backup in Sagna.
Gibbs and Monreal are two strong options to have at LB, there is no issue here.
I'm more worried about RB, especially with Sagna looking very good filling in at CB. Jenkinson is raw, but has shown he can put in against good sides, he just has to continue to develop. Flamini can also play RB (and LB).
A certified WC CB and/or RB would have be amazing, but you can't win them all.