Maybe wait and see in January? We have four CBs and should be able to survive until then, right?
If anything it's a lot harder to buy/bring back players in January. It's a rip off month and a period of time when clubs are trying to settle, not push away players, let alone a main defensive player from Atalanta who seem to be doing good.
I read some news this morning how there's a chance we won't buy any CB as we're rely on the current rooster, though, but I doubt that means we're getting Caldara in January.