But the Knights will not impose additional punishment on Hetherington over his bizarre antics during round seven, satisfied the prop's "contrition is high" amid his one-game suspension from the NRL.
Hetherington and Mahoney were sin-binned in the dying moments of Canterbury's' 36-12 NRL win on Sunday following a melee between the sides.
Things threatened to escalate as Hetherington waited for Mahoney in the tunnel, bouncing on his feet like a boxer and intimating he was ready to throw a punch.
Hetherington then appeared to push Mahoney in the chest before the pair were separated by nearby NRL officials.
Parr and Knights coach Adam O'Brien have each addressed the incident with Hetherington, who received widespread media scrutiny this week.
"The facts of the matter are he should've went straight to the dressing room and not been baited," Parr said.
"He needs to be better than that, I've had a good conversation with him as has the coach. We expect that that won't happen again."
Hetherington's discipline frequently landed him in hot water early in his career - across his first 40 NRL games Hetherington was charged eight times by the match review committee.
But the 27-year-old has largely cleaned his act up since arriving at the Knights last year and was an important member of their middle rotation on the run to the most recent semi-finals.
The grade-two contrary conduct charge Hetherington received on Monday morning marked his first time being cited by the match review committee since arriving at the Knights.
"His discipline is one area that has improved so it was a bit of a throwback for him. We've got to make sure there's no more," Parr said.
But Parr is confident Hetherington had learnt his lesson and would not need extra punishment from his club.
"Right at this point we haven't decided to sanction him," he said.
"His contrition is high. He's been the subject of a lot of scrutiny from the public and the media and the NRL have sanctioned him so whilst we're not happy with how he's gone about his business there after he got sin-binned I don't think inflicting any further punishment on him would achieve too much at this stage."
Parr's comments come as Kalyn Ponga braces for 12 weeks on the sidelines with the Lisfranc injury he suffered against the Bulldogs.
The talismanic Knights and Queensland fullback is set to miss the entire State of Origin series and a crucial period of the Knights' NRL campaign, which has begun in lukewarm fashion.
"He's obviously very disappointed," Parr said.
"He'll play football again this year so he's very positive about that. That's some good news for him.
"Hopefully our team can string enough wins together over the next few months that they're in finals contention when he comes back."
