In Ashley Cole, Chelsea have one of the world's top left backs. He's a major attacking threat while remaining defensively stout - the sort of player every other team wants to spend millions on acquiring and resources nullifying during matches. Unfortunately for the Blues, he's already starting to slow down and is somewhat prone to injury, meaning his backups will almost certainly come into play at some point this season. Cole will probably play 30ish league games this season (presumably very well indeed), but there are a couple of scenarios in which he goes down early and Chelsea have to struggle to replace him. These are very bad scenarios, because we've just sold Yuri Zhirkov.
Zhirkov's departure means that Cole's primary understudy will be one of Ryan Bertrand and Patrick van Aanholt. Bertrand is the choice if you're looking for a solid two-way player, and van Aaholt is your man should you prefer defenders who have the defensive ability of a dessicated stoat but can attack like demons. Personally, I find van Aanholt more fun, and we might end up with him anyway, because Bertrand sounds like a good bet to get some time out on loan.
Oh, and there's always Paulo Ferreira.
loyal brave and true loyal brave John Terry leads Chelsea's crop of centre backs. I suspect if you're reading this blog, you have some idea of who he is. If not, he is a crazy man who trundles around slowly hurling himself with great violence at any threat to Petr Cech's goal or England's decency. Terry, of course, is beset by enough chronic injuries to cripple an elephant, so expect him to miss some time.
Alex isn't exactly the healthiest chap around either. He's also a stalwart defender, and before the arrival of fellow Brazilian David Luiz he was Terry's regular partner in the centre of defence. Strong positioning, tackling and aerial ability make up for any lack of pace, but Alex's main weapon is the ability to hit the ball at Mach two from set pieces. Alex will probably serve as the third-choice centre half, becaause David Luiz is amazing.
And yes, he really is amazing. The 24-year-old, a 25M buy from Benfica in January, is one of those special players who makes games far more fun. Easily the best pure defender on the roster when he's paying attention, his main flaw is that every now and then he stops paying attention and/or does something hilariously stupid, like giving away last minute penalties for no reason or forgetting where to stand. He makes up for this with an array of spectacular skills, ranging from his patented overhead kick crossing, pinpoint finishing on the volley, 60 yard raking passes and the ability to smack Wayne Rooney in the face without getting in trouble for it. David Luiz is ace.
We may also see some Branislav Ivanovic here, although I'd expect him to get more time at right back. Ivanovic is also a sublimely capable defender, and Chelsea will be absolutely fine if he slots in there. With four quality centre backs, the Blues have plenty of depth.
That might be improved depending on whether 22-year-old Slobodan Rajkovic can manage to obtain a work permit. The prospect has impressed during pre-season, and could slot into Alex's role without breaking a sweat, possibly freeing the Brazilian up for a move away. If he doesn't get a permit, Rajkovic will probably have to go out on loan yet again.
Nathaniel Chabolah rounds things out, but while the 16-year-old is awesome, he's unlikely to get too much playing time in the first squad. It's not his time quite yet, although he'll probably make his debut if Chelsea manage to play in any irrelevant games this year.
Despite links with both Gergory van der Wiel and Samuel Inkoom, of Ajax and Dnipro respectively, Chelsea go into the season with the choice of Branislav Ivanovic and Jose Bosingwa as right backs. Ivanovic is the clear pick when staunch defending and aerial prowess is required, but he's nowhere near as good as getting forward as Bosingwa is.
Since coming back from an injury sustained in October 2009, Bosingwa's been a bit (ok, a lot) of a liability defensively, but he's been impressive in the preseason, and if he reverts to being a right back you can call two-way without sniggering too hard, that'd be pretty useful. And if not, Inkoom!
Oh, and there's always Paulo Ferreira.