The Blues board made their decision to put Barton up for sale after his training ground bust up with team-mate Ousmane Dabo.
Barton’s agent Willie McKay said: “What’s happened is very unfortunate.
“I have spoken to City’s chief executive, Alistair Mackintosh, and he told me they want the price that is in Joey’s contract.
“If City get the £5.5m they will be happy and Joey will be sold.”
Everton, Sunderland and Tottenham are all interested in the England international.
