We could argue about whether or not he'll end up being the new Beckenbauer (or Koeman!) til the cows come home but no one knows how he'll turn out. If he doesn't want to play for us let him go and get the best deal for the club. If that happens to be a world record for a defender I can't see how anyone can complain about that, especially for a kid who can't get into the national team and is still very much a work in progress.
Looking at the players we've sold for over £10million in the past I'd say on the whole we've done pretty well out of the deals..
Fellaini £27.54m - good deal for us - been in and out at Utd and future uncertain
Rodwell £12.75m - great deal - 16 games in 2 years for City - sold on to Sunderland at a loss
Arteta £10.5m - did OK for Arsenal without setting the world alight - decent price for us though
Lescott £23.38m - did well for City won a few trophies but let go on a free at the end of his initial contract
Andy Johnson £11.38m - 27 goals in 112 appearances over 4 years for Fulham says it all - very good business for us
Rooney £31.45m - the one that got away but despite all his success not sure he turned into the world legend we all thought he might be
Jeffers £13.01m - 8 goals in 39 games over 3 years for Arsenal sold for £2.6m to Charlton - exceptionally good business
Need to balance that with the likes of Eric Dier and Shkodran Mustafi whom we let slip through our fingers but I think they prove how difficult it is to predict just how good a career any young player with potential might have.
Bottom line is if anyone doesn't want to play for us, get rid and get the best deal possible. I think history shows our record in doing so is pretty good.