Senior NRL stars have endorsed the proposal of an 18th man to cover players ruled out due to head knocks or foul play, provided measures are put in place to ensure it can’t be manipulated to earn a competitive advantage.

The ARL Commission will meet on Tuesday to discuss introducing a concussion substitute as well as player welfare and injury rates after a spate of high-profile casualties over the weekend.

The idea has been raised at NRL competition committee meetings in recent years but has been met with resistance based on what NRL head of football Graham Annesley described as the "potential to create for gamesmanship" on Monday.

Veteran five-eighths Cody Walker and Kieran Foran hold the same concerns.

Walker suggested an 18th man could only be used if a player is injured by foul play, such as when Parramatta's Ryan Matterson suffered a concussion from dangerous contact that led to Melbourne back-rower Felise Kaufusi copping a two-match ban.

"I think the 18th man is a good idea for the game but I suppose you have got to make sure that you can’t rort the system and all of that sort of stuff," the South Sydney pivot said.

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"I feel that it has to come from foul play that the 18th man can come on.

"I don’t know whether the guy who comes off has to miss the next week, that might stop the rorting of the system but I don’t know.

"There are so many questions you can ask about it but no one has the answer."

The AFL announced its introduction of a "medical substitute" two days before its season kicked off, with a club doctor needing to rule a player as "medically unfit" before a substitute can take the field.

For all injuries other than concussion, a subbed-out player can return to play in the next game if his recovery is ticked off by the AFL's medical officer.

Foran sees the NRL's doctors present at every game holding a similar responsibility in enforcing any concussion substitutions.

"I think the game's done a hell of a lot of work around the protocols, looking after player safety there," said Foran.

"Having that 18th man, for that particular [issue], is a good idea. I'm sure there's independent doctors on the sideline that can make those rulings to avoid the rule being manipulated.

"You're always going to try to find an advantage as a club aren't you? But I think having independent doctors and the NRL medicos being able to make that call, that takes that manipulation part out of it."

Annesley's football department will provide the ARL Commission with "as much information as we can" regarding game speed, injury rates and the impact of new rules in 2021.

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NRL data showed across the first two rounds, ball-in-play time this season had not changed from last year's average of 56.2 minutes per game.

He added on Monday that those figures did not change significantly in round three.

Concerns around injury rates were raised last year when the six-again rule was first introduced, with 2020 a unique NRL season given the COVID-19 layoff and rescheduling that impacted player preparations and pre-seasons.

"You have to look for unintended consequences as well for every decision you make and the commission has to consider all those factors before you they make a decision," Annesley said of introducing an 18th man.

"It's something that needs to be carefully considered, we need to provide as much information as we can."

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James Tedesco and Josh Morris were part of a Roosters outfit that finished with only 12 fit players against South Sydney, while Canberra and Cronulla had only one bench player between them for the second half of their respective games on Saturday.

While Tedesco can't "see the harm" in an extra substitute being available, Morris thought added fatigue had been created by the six-again rule.

Manly skipper Daly Cherry-Evans stressed he hadn't played in a game impacted significantly by injuries this season.

But the RLPA president would prefer to wait for a bigger sample size before determining whether the NRL's new rules have sped the game up too much.

"It's not too fast. It's quick but that's where the game's at so you've got to adapt and keep up," Cherry-Evans said.

"I'm sure the teams that are winning aren't complaining about how quick it is.

"At the end of this year if there's a correlation then maybe we do have to sit down as a game and go, 'all right what are we trying to get out of this?'

"Because we've got a pretty good product, but how far are we going to push it? Right now I do believe we're still adapting to it all."

Sharks winger Ronaldo Mulitalo was one of the 13 players in his team who had to play the full 80 minutes on Saturday night against Parramatta after a spate of first-half injuries.

Cronulla played without a fit player on the bench for the entire second half of their gutsy 28-4 loss to Parramatta after Wade Graham, Briton Nikora and Will Kennedy failed HIAs and Sione Katoa injured his knee. The Eels lost Mitch Moses to concussion while Maika Sivo later recovered from a head knock.

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He said "some of the boys are not happy about" the game being faster in 2021.

"I think the biggest thing is [restarting play after] kicking the ball out … I just want to question, who gets the advantage?" Mulitalo said.

"Is it the defence or the offence? Because ultimately, you're running into a set line. It's different to running three-on-three [from a scrum]."

Sharks utility Connor Tracey, who moved from centre to fullback against the Eels, hasn't felt more fatigued than usual.

"I think the speed of the game hasn't increased as much as people say it has," he said.

"I'm sure there are some stats about it ... It's only round three, so as we go on we'll probably feel [the fatigue] more."