State of Origin coaches Laurie Daley and Billy Slater have responded to the Ashley Klein betting controversy, backing him to do a professional job in Game 2 of the series, which will be played tomorrow evening in Melbourne.

It was revealed last week by the Sydney Morning Herald that Klein has lost over $400,000 betting on horse and greyhound racing.

He has never placed a bet on an NRL game, and the NRL were aware of the situation, with the game's governing body standing behind their appointed referee for the second game of the series.

There is no indication or claim by this publication or others that his refereeing of NRL games or representative fixtures has ever been impacted, and Klein put out a statement to that effect last week after the report surfaced.

Both Origin coaches downplayed the incident in a joint media opportunity on Wednesday, with Billy Slater going as far as to say it hadn't even been discussed.

"To be honest, I personally think it's unfair to have something personal like that to be revealed publicly. It hasn't been discussed within our camp,” Slater responded during the event after being quizzed.

"That's my personal position with it, I think it's quite unfair on him."

Men's State Of Origin – NSW v QLD: Game 3

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Laurie Daley, who is under pressure to win the series given his horror overall record as NSW coach, agreed with Slater.

"I agree with Billy. It's challenging when things like that get brought up, and I just hope he's got the right support and the people around him," the Blues boss said.

"We've got no concerns with Ashley being apart of the game."

Klein, who refereed the series opener in Sydney, was involved in a controversial send-off of Kalyn Ponga after he wiped out Tolutau Koula.

The referee heads into his 22nd State of Origin match on Wednesday evening.