Knights forward Jack Hetherington is facing a one-game suspension for his altercation with Canterbury hooker Reed Mahoney on Sunday.
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The NRL match-review panel has issued Hetherington with a grade-two contrary-conduct charge, after he confronted Mahoney outside the Bulldogs' dressing room and appeared to challenge him to a fight.
If he pleads guilty, he will be sidelined for one match.
If the Knights opt to challenge it at the judiciary and lose the case, he will face a two-match ban.
Hetherington and Mahoney were sin-binned late in the match after a melee, during which they clashed verbally.
Video footage emerged later of Hetherington apparently approaching Mahoney in the players' tunnel, appearing to shape up, before Bulldogs staff intervened.
At the time, it was unclear if he was serious or it was just banter.
Mahoney was charged with grade-one contrary conduct but can escape with a $1000 fine.
Knights coach O'Brien said "I don't even know what you're talking about" when asked about the incident after the match.
Canterbury coach Cameron Ciraldo, who coached Hetherington at Penrith, was inclined to give the fiery prop the benefit of the doubt.
"I don't think it's too serious," Crialdo said.
"Jack's a good fella.
"I've known Jack for a long time. He's a good guy.
"Sometimes he gets emotional, but he's a genuinely good person, so I don't think there'd be too much in it."
O'Brien said Hetherington's sin-binning was evidence of a "frustrated" team.
The fiery prop was suspended a number of times earlier in his career, but had managed to avoid judiciary scrutiny since arriving at the Knights last season, despite a couple of stints in the sin-bin.
His likely absence for Sunday's clash with the Dolphins will further deplete a Newcastle team already without Kalyn Ponga, who is awaiting a prognosis after suffering a foot-ligament injury.