McDermott will now hold talks with the 25-year-old, who only joined the club from Newcastle in the summer.
"He made a decision that his head wasn't right to travel," McDermott said.
"Everyone has got to be going in the same direction, that's really, really important for me as a group, and we have had that for a period of time.
"You have to put yourself up to be selected in each and every game, and that means every player.
"Any player has to be part of what we are about. We can't deviate from what we have been about over the last three years.
"We are very much about the group - we have to be. We all have to pull in the same direction. It's probably not a conversation for this evening, but it's something that we need to address in the week."