Matt Matt Ritchie and Jamaal Lascelles were involved in a training ground bust-up, according to a report.
Lascelles, Newcastle United's captain, missed last weekend's 2-1 defeat to Chelsea because of an ankle problem.
However, the defender had also had a disagreement with manager Rafa Benitez over tactics ahead of the fixture.
Benitez had fielded a five-man defence against Chelsea.
Speaking after the game at St James's Park, Benitez said: "All my life I like to talk with players. We decide with what we have to do. Every one knows that. If players have different opinions then we have to speak about it, that’s it, and then we stick to the plan.”
Lascelles praised the efforts of his team-mates on Twitter after the game.
"Frustrating not to be able to play due to a slight ankle injury," tweeted the 24-year-old. "Great effort from the boys against a top team."
Lascelles, linked with a number of clubs this summer, had trained for most of the week before reporting his injury.
And the Daily Mail report that Ritchie confronted his skipper on the training pitch after Lascelles "voiced his disapproval over Benitez’s decision to play with a five-man defence".
The pair, it's claimed, were separated by team-mates and shook hands afterwards. Benitez also spoke to Lascelles, who was handed the captain's armband two years ago.
Lascelles could return for Saturday's Premier League game against Manchester City at the Etihad Stadium.
“The doctor told me he is much better than he thinks," said Benitez. "He's waiting for a scan.
"I talked with him before the game, because he supported the team. I spoke to him when he was leaving, and (Tuesday) morning he was talking three or four times. He's waiting for his partner to have a baby in the next few days."
Winger Ritchie will miss tonight's Carabao Cup tie with a knee problem.