Johnson, 28, will almost certainly receive a hostile reception but he is adamant it was cash-strapped Blues' decision to sell him following their relegation, rather than him forcing their hand.
The central defender said: "The club had been relegated and I was asked if I'd like to leave.
"It wasn't a case of me banging the door down saying 'let me leave'. It was a gesture from them saying 'listen, we're in a crisis and we need the money, so if you can get yourself a club and get us some money, then off you go'.
"They didn't want to see their best players leave but, at the time, it was out of my hands. They cannot come back to me and say it's not true because I'll beg to differ. Those are the reasons."