I'll lay down my marker early. Manchester City can't afford to lose Carlos Tevez this summer. He is quite simply one of the best strikers in the world and perfectly suited to drive City deep in the Champions League.
So what is it that makes Tevez so valuable? Two things are obvious: goalscoring prowess and workrate. But there's much more to him than that. Other than Messi he's the best player in the false 9 position on the planet.
What's the false 9? Simply, a striker with license to constantly roam both deep and wide in order to generate attacks high up the pitch and pull the centre backs out of position as they desperately seek 'their' man. City have built their attacking play around this idea - Tevez dropping deep and providing huge gaps (and pin-point service) for Silva, Johnson (reverse wingers - another feature of a false 9 formation) and, especially, Toure to gallop on to.
Later in the season, with Milner playing alongside De Jong, we looked liberated. Both players started to look for quicker attacking options rather than the walking-pace build ups we'd become accustomed to. Even with Tevez not in the team and a more traditional centre-forward we looked more menacing. Some might put that down to Tevez himself being the problem. Absolutely, definitely not so. With Yaya, or Milner, or perhaps Daniele Di Rossi partnering De Jong in the double pivot, coupled with blinding, bewildering movement from Tevez, Johnson, Silva and perhaps Sanchez, we'll be much, much better next year and it'll be Tevez that makes it all possible.
Movement, pace, distribution, workrate, goalscoring ability, tactical awareness. Only Messi is better.