The City boss said: "I'm disappointed I had to do that to a magnificent professional, but I needed to change things to try to wake up the rest of the back four.
"Any of them could have come off and Richard was unlucky it was him. I have apologised to him in the dressing room, but when you are a manager you have to do things to try to change the course of the game.
"Maybe if he becomes a manager he will understand one day."