What next for Chelsea after selling David Luiz?

There's an interesting distinction between buying and selling players in the transfer market. In individual players you have more or less known quantities; spending money bringing someone in therefore trades an uncertain resource (cash on its own doesn't help you win football games) for a more robust one. You can, as Tottenham Hotspur demonstrated rather thoroughly last summer, make a great deal selling a player and mess it all up by spending unwisely.

A cursory glance at Chelsea's finances shows that the club did not need to sell David Luiz to Paris Saint-Germain; we can therefore assume that the money from the Brazilian's sale will be reinvested back into the squad this summer, alongside the cash we already had on hand from the Juan Mata transfer and in addition to whatever else we had earmarked for upgrades. This is an enormous amount of money, but at present it's essentially footballing potential. We need to turn this rather fluid resource into real upgrades, and we should do it as quickly as possible.

The economics of the Mata and David Luiz deals favour Chelsea, and they favour us pretty heavily. But that will only matter if we have a plan for the summer and execute it properly. Let's sketch out what the plan should look like quickly.

First and most obvious is a true striker. The Blues were crippled by a lack of ability to convert half-chances at a rate anything like their title rivals last season; a goalscorer who can create space in the box for the likes of Eden Hazard and Oscar to play with. This is obviously going to happen -- Jose Mourinho's been talking about it for the better part of 2014 -- and it's probably only a matter of time until we unveil Diego Costa as a Chelsea player.

Part two of the plan is murkier. We've been linked to a big-money left back, Rapfael Varane and even another striker, but for me spending big money there is at best a distraction and at worst a crippling waste of resources. With David Luiz gone, we need an elite midfielder to replace him.

No, David Luiz was not an elite midfielder. But in what I'd argue were our best games of the season, at least from a performance standpoint (Liverpool at home, Manchester City away, Arsenal at home), he played like one. If we want to match the level we were at in those matches next season, we have to ensure that our midfield is up to scratch. And right now it isn't. Nemanja Matic is a lock to start, but none of Frank Lampard, Ramires and John Obi Mikel were anything like convincing last season, and it wouldn't be a shock to see any or all of them out this summer*.

*Marco van Ginkel is at this point a wild card, and not to be counted on.

Despite the complaints from the media and some of the more fickle fans, Chelsea were a very, very good team at points last year, capable of dominating games against even top opposition. But that dominance relied on David Luiz having a good day. Had every day been good, he'd never have left the club -- his inconsistency ultimately doomed him to a life of fame and wealth in Paris -- but acknowledging that he's an erratic player doesn't mean we ignore just how good he made the team when he was on.

There are only a handful of players in the world who can match (or even come close to matching) David Luiz at his best while avoiding the pitfalls of the 27-year-old at his worst. Fortunately, we can now afford all of them. Turn this money into a world-class partner for Nemanja Matic, buy a striker, and this summer will have been a success. But if midfield's neglected now, we're in for a rough 12 months.