Newcastle may take action against Charles N'Zogbia after he refused to sit on the bench against Watford.
The midfielder is reported to have stormed out of Vicarage Road after only being named as a substitute.
Magpies caretaker-boss Nigel Pearson said: "He was originally on the bench but he didn't really want to be there.
"I've no idea whether he stayed at the ground to watch the game. Will there be disciplinary action? That's something for next week."
Pearson added: "You can make your own judgements about it but it is very important that everyone associated with the club acts in a professional manner."