The 19 year-old's contract expires this summer, but as he is under 24, he is not available to sign on a Bosman-style free transfer.
The two clubs have failed to reach an agreement on a suitable compensation package. City are looking to get a 'development fee' of around £10 million, but Chelsea's valuation is thought to be £3 million.
Nothing official from either club's websites, but it is a story that is now being widely reported with the agreement (or decision) of a fee the only thing now outstanding.
What will be interesting is the undoubted recriminations from both camps as to exactly where the blame lies for the failure to sign him to a new deal. I've written plenty before as the saga dragged on but we should see more come out over the next few days or so.
As big a potential loss as this could be, we are in a fortunate position that in terms of bringing players to the club the loss may not be anywhere near as damaging as it once might have been.