Birmingham midfielder Nicky Butt has been reportedly fined £80,000 for walking out on the team before Monday's 3-0 defeat at West Ham.
Steve Bruce's son played ahead of Butt against West Ham
The punishment of two weeks' wages came after the on-loan Newcastle midfielder issued an apology.
"After being told I was not to be part of the West Ham game, I made a decision I regret," he said in a statement.
"I would like to apologise unreservedly. We are in a battle and it is important we all stick together."
After the defeat at Upton Park Bruce said: "I will be doing my own enquiries into it and we will deal with the matter over the next 48 hours in our own internal way."
Bruce picked his son Alex - normally a defender - in midfield ahead of Butt.
Butt missed Birmingham's game against Reading in the FA Cup on 7 February because of a dead leg.
Bruce added: "Nicky didn't ask for permission, he decided on his own bat to leave and go home.
"Alex was a makeshift midfielder with the injuries we've got but I wouldn't have thought that played any part in Nicky's decision. Not at all.
"Nicky didn't play in the last game because of injury and we decided that he was not going to be involved in the 16.
"He travelled with the team and when he wasn't involved with the 16, he left to go home."
Bruce revealed that he could understand why the former Manchester United star was frustrated.
He stated: "Nicky went home from the team hotel. Of course, that is not normal but you can understand his frustration and disappointment.
"He felt he would be better going and watching it at home rather than be with us. It is not ideal but that is what has happened.
"I will deal with it in a way I see fit. It is a bit difficult now with emotions running the way they are because I've just seen my team get stuffed."