"Basically the two clubs are negotiating," Di Matteo told his club's official website.
"His team-mates are fighting for a cause. I didn't feel it was right for him to be involved last night.
"He's been a great professional for us. I spoke to him before the game.
"There has been a lot going on for him in the last five or six weeks but, once again, I have to emphasise he's been very good for us.
"He's been a true professional and it was my decision to pull him out last night."