An 18th player to replace NRL players ruled out of matches due to concussion will be on the agenda as will third-party doctors when the competition committee meets in April.

Calls have grown for an extra player to be available when a player's game is ended by a head knock with teams enduring reduced numbers on the bench after a series of incidents this season, while other have suggested an independent doctor would be better placed to assess concussions.

Despite bench depth being tested,NRL chief executive Todd Greenberg is understood to be reluctant to make sweeping changes, cautioning against major shifts around concussion rules.

"We are open to independent doctors, we've got to look at things like an 18th player," Greenberg told Fox Sports' League Life.

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"(But) you have to be very careful. You have to spend a lot of time making the right decision."

Greenberg reinforced his view that calling for third-party doctors to assess concussions undermined the job club physicians were doing.

"I do warn people though ... if you're asking for independent doctors, what you're saying is the current doctors aren't independent," he said.

He defended the NRL's decision to hand out $350,000 worth of fines to three clubs for breaching concussion rules earlier in the season.

"The incidents that I saw in round three were far more disturbing for me than others," Greenberg said.

"I haven't seen incidents as difficult to watch as I saw... particularly around those three that were issued breach notices where players were laying motionless on the ground.

"At some point I felt the game had to make a statement and we did."

Greenberg singled out the Josh Dugan incident, in which the Dragons star continued playing after laying motionless after a hit, as one of the reasons he was moved to hand out a stiff penalty.

"The response is back from the Dragons and I'll assess that, but from what I saw that constituted a breach of our rules and that's why I acted," he said.

He said the money from the hefty fines would likely be poured into the league's concussion research program, which allows doctors to view head knocks on the sidelines.