According to The Independent, Joey Barton clashed with Sam Allardyce before Newcastle played at Wigan on Boxing Day.
Barton is understood to have disagreed with Allardyce's decision not even to have him on the bench for the Wigan game.
The club said that Barton had an ankle injury from the game against Derby County three days earlier, but it is understood that it was never Allardyce's intention to name the midfielder in the squad for the Wigan game.
Having travelled with the Newcastle players, Barton told Allardyce he was unhappy he was being rested when the team was announced before the match.
The incident was witnessed by some members of the coaching staff in the dressing room at the JJB Stadium.