Australian coach Mal Meninga has hit out over criticism of the decision to award Billy Slater the Wally Lewis Medal.

Meninga, who voted on the award for the Origin man of the series with Kangaroos selectors Darren Lockyer and Laurie Daley, has defended the panel's decision based on a points system, taking offence to those questioning the integrity of three of rugby league's greatest players.

"Everyone has an opinion and that's fine," Meninga told NRL.com.

"But when you start to question our personal integrity around how we do things, that's unwarranted. That upsets me the most – that our integrity has been questioned. There's no bias. It's a decision by three individuals who I think have a pretty good knowledge of the game."

The process of deciding on the medallist was recently overhauled, with the three panel members voting on a 4-3-2-1 points system (four being the best).

"The process itself – we have to sign a confidentiality agreement to keep the process in check," Meninga said.

"We vote independently. Through that process we don't collude and we don't talk. The points are collated after each game. Billy polled very well in game two. We had opinions that he probably should have got man of the match in game two despite NSW winning the game and the series.

"How can you question giving Billy man of the match on Wednesday? I know Tom Trbojevic was great but with due respect what we see in the game is a little different to what other people see."

It's understood James Maloney polled very well in the first two games but didn't do well enough in the loss to Queensland in game three to claim the medal. Given NSW had several great players throughout the series, points were spread across the team.

"That's exactly what happened," Meninga said.

"But if I'm a coach of a footy team and I have 17 players making a great contribution, that's what I want."

Slater has shrugged off criticism about the controversial decision to name him the player of the State of Origin series.

"You take it with a grain of salt," Slater said on Thursday morning when asked about the negative feedback.

NRL CEO Todd Greenberg said the three panellists could not have better credentials for being the judges.

"Three of the most preeminent minds in the game voted for that last night," he said.

"We review everything at the end of an Origin series and I'm sure that will be part of it but you can't question the integrity of the three men making the decision.

Greenberg said it would not be fair to ask them to reveal who they voted for in the three games.

NSW coach Brad Fittler and five-eighth James Maloney expressed their surprise with the decision to overlook a Blues player in favour of Slater as the Wally Lewis Medalist while former players and social media lit up with criticism over the decision.

Daley said on Thursday morning's Big Sports Breakfast on Sky Sports Radio: "The rules are that after every game, Mal Meninga, myself and Darren Lockyer put in 4-3-2-1. Four being the best player, three being the second best and so on.

"The player who accumulates the most points out of those three games, when you total them up at the end of the series, is the man of the series and the Wally Lewis Medallist.

"And the guy that totals the most amount of points in that particular game wins man of the match. Billy Slater won fairly under that system."