Brad Fittler has warned the NRL not to follow the AFL into introducing an injury or concussion substitute, leading calls not to take the war of attrition out of the game.

The AFL’s decision to rush in separate injury replacements on the eve of rhe 2021 season for players ruled out of games has sparked debate in the NRL.

Ryan Matterson, Adam Reynolds, Nathan Cleary and Jaxson Paulo all had their games ended early by head knocks in round two.

Warriors coach Nathan Brown has long pushed for concussion substitues, arguing that teams should be able to take two additional reserves into matches to cover all bases.

But NSW State of Origin coach Fittler is among those not so sure.

“I feel like the four (men on the bench) are enough,” Fittler told AAP.

“Occasionally you are going to be down to one reserve, Brisbane were last week (in round one). But that’s happened in the past, it’s not new.

“If they saw fit and felt like the players’ welfare wasn’t being looked after then I could understand if they did it.

“But I haven’t seen teams finish games with 12 players because of four or more players being injured..”

The AFL’s change came after a strengthening of concussion protocols, and was initially only set to cover head knocks before coaches pushed for all injuries to be included.

Seven injury substitutes were used in the first six games of the opening round, but there are fears that clubs could potentially cheat the system.

And Fittler expected that would likely happen in the NRL, given the importance of fatigue and the war of attrition.

“I think it would be a crying shame if clubs started abusing the rules,” he said.

“That would be sad if they started abusing the concussion rule.

“But that’s part of the puzzle of picking the bench, having someone who can cover (positions). That’s part of the puzzle for coaching and part of recruiting.”

Sydney Roosters coach Trent Robinson this week said he was undecided when asked about the issue, also concerned about how introducing a fresh man would change the game.

But he does believe that the rule could make clubs more willing to protect concussed players.

Another NRL coach also privately pointed out to AAP that most clubs already carry a bench player that is rarely used, and that the ability for teams to win under the adversity of a reduced bench is valuable.

Cronulla veteran Wade Graham also warned against the move, pushing the fatigue factor and concerned clubs would take advantage.

“Rugby league is a collision sport, it’s a war of attrition,” he said.

“A part of the fabric of the game is not to battle though injury but battle though pain and to keep going.

“I’m always willing to look at ideas … but I think the toughness in the game is something we should admire, not something that we should take away.

“You look at the flip side, how do you police people taking advantage of the extra sub on the bench.”

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