Not that worried. Talent but no team
The next 7 behind that team, forming a regular rotation of 18 (assuming Mikel leaves):
-- Cech, Ivanovic, Ake, Ramires, Salah, Schurrle, Torres
-- good, good, 19, meh, meh, good, meh
And the youngsters behind that rotation? (because someone is going to get injured / suspended)
-- they're all out on loan (or will be again)
They had 8 defenders last season. Already sent 1 on loan (Kalas), lost 2 (Cole, Luiz - although I'm not sure you could call him a defender), and now they're left with 5. Of the remainder, Ake is 19 and Terry is 33 and certainly going to see more mistakes start to creep into his game.
Solid 14 players, but after that, I'm not sure. Of course, they could decide that some of their guys on loan could be ready, but looking at the list up there, there really isn't a slot of any of them to go into the regular 18 right now, except at CB. Unless they're that good that they could displace some of the incumbents.