He's signed a contract. If he wants to leave but City say no then he should still provide the club with £300,000 worth of effort, ability and attitude every week. If he doesn't and agitates for a move, gets his agent to run his mouth off and disrupt the squad then most clubs in the world would have to face financial reality and sell him on.
City aren't in financial reality and it would do the game good for player / agent power to be reined in every now and then as at the end of the day whether it comes via the TV companies, gate receipts or sponsors it is our money. The fans deserve a little more respect.