Concussions and the process involved with examining players who have suffered head knocks in games have come under scrutiny in the opening month of the season.

It has forced the NRL to undertake a review of the process, with Greenberg organising a phone hook-up with each of the club's chief medical officers for this week.

Fairfax Media understands the NRL wants to implement some clarity around the rules, likely to crack down on certain physical indicators to determine whether a player is able to return to the field.

If a player is visibly struggling to get back to his feet or stumbling around the field like Adam Reynolds was in the round two fixture against the Sydney Roosters, it's unlikely he will be allowed to return to the field under the new guidelines.

In its current format, players are allowed to return to the field after completing a SCAT test and receiving medical clearance from the club doctor.

However the NRL could implement a blanket ban over players returning if they show any of the indicators they are cracking down on. Greenberg said the NRL initiated a review of the concussion rules last week to determine whether any changes are necessary.

Greenberg will undertake a review in consultation with the clubs, admitting he'd prefer to continue working with the clubs than introducing independent doctors to examine players.

"One of the aims of that review will be to minimise any confusion about when a player should be removed from the field and allowed to return," Greenberg said. "The NRL's preference is to work with the chief medical officers of the NRL clubs, rather than introduce independent doctors. I will be talking to the chief medical officers of all 16 clubs this week as part of our review."

Greenberg said he would contact Manly coach Geoff Toovey this week to discuss the concerns the Sea Eagles mentor raised after his side's loss to the Dragons in Wollongong on Saturday night. Toovey was frustrated his star halfback Daly Cherry-Evans was taken from the field when his side was chasing victory in the final minutes of the game at WIN Stadium, adamant doctors were making decisions in fear of the repercussions.

"We've got doctors now panicking on the sideline because they don't want to get in trouble," Toovey said. "They're just reacting to anything that happens. It has to be sorted out one way or another. To me, it's just people worried about getting sued."

Asked if he had a solution, Toovey said: "No, I don't  It's not up to me to have a solution. It's up to the game as a whole. I'm not in charge of the game.

"The doctor thought [Cherry-Evans] may have been concussed so he told the trainer to go out and get him off. They know the chief medical officer of the NRL was here tonight on the sideline and they're all panicking. They don't want to get the club sued, they don't want to be liable for anything. It's just crazy."