We don't have nothing. We have Piqué, Puyol, Mascherano and Bartra. They're not the best bunch of CB's right now but our targets are generally shit as well, they'll quickly get exposed within our system and we'll see them for what they are, other average CB's.
Don't get me wrong, it's not like I think signing a guy like Mathieu would be a stroke of genius or anything like that. In fact, I think him (or someone similar) being our CB signing would be pretty bad. Signing Matheiu would, however, be better than signing no one, since someone like him would add a bit more depth, at the very least.
It's not like it has to be Mathieu or nothing though. There are better options like N'Koulou, Zouma and Doria. They're all young (especially the last 2), fairly cheap and attainable. N'Koulou is Ligue 1's second best CB and the other 2 have a lot of potential.