McGregor copped a breach notice proposing a fine of $10,000 after labelling the referees as "embarrassing" and "incompetent" after the round 21 loss to last-placed Newcastle. After considering the club's response, the NRL opted to fine the Dragons just $5000, with the remaining $5000 suspended pending further breaches.

In coming to the ruling, the governing body took into consideration that it was McGregor's first offence and that his responses were prompted by a series of questions regarding the whistleblowers, rather than a premeditated attack on officials.

Asked if the referees got it wrong, McGregor said at the time: "Definitely - I think that anyone who knows rugby league would agree because the ball went back on the [Jason] Nightingale one and it should have been overruled and it wasn't and [Trent] Hodkinson took a dive."

Pressed on if the decisions were especially disappointing, given the bunker had time to deliberate on them, he said: "It is. When you spend millions of dollars, it is."

It's the second time this year the NRL has suspended a portion of a fine meted out to the Dragons. The Red V was slugged $100,000 for non-compliance with concussion protocols in March, although half that amount was suspended pending further breaches.

North Queensland coach Paul Green wasn't as fortunate as McGregor. The NRL settled on a $10,000 fine for the Cowboys after Green accused whistleblowers Ashley Klein and Alan Shortall of presiding over the "worst refereeing display ever" in their loss to Penrith.

"I said to the boys after the game I've never been involved in a game where so many things have gone against us ... it's just a shame the refs ruined the game," Green said at the time.

The NRL weighed up the fact that Green had heavily criticised the match review committee in 2014 before opting to fine the premiership-winning mentor the full $10,000.

"The NRL has suspended half of the Dragons' original breach as it was a first offence for coach Paul McGregor," an NRL spokesman confirmed.

"The Cowboys' fine was not suspended as it was coach Paul Green's second offence in the past three years.

"All coaches should be aware that we will continue to ensure the integrity of the referees is protected in the lead-up to and during the finals series."

Canberra coach Ricky Stuart, who has been fined a record $125,000 throughout his career for his attacks on the referees, narrowly escaped another hit to the hip pocket for his outburst following his side's loss to Melbourne.