The NRL has warned that it will impose heavy penalties and strengthen its concussion policy if necessary to protect player welfare.

The warning comes as the league investigates the circumstances surrounding South Sydney halfback Adam Reynolds and Parramatta hooker Nathan Peats returning to the field after copping head knocks in recent weeks.

NRL head of football Todd Greenberg said on Monday he was concerned about several serious head injury incidents which had occurred in the first three weeks of the season.

Those incidents were being investigated and action would be taken against any club which has breached the rules.

Both the Reynolds and Peats instances drew criticism, but their clubs insisted they had correctly followed the concussion protocols before deciding they could go back on the field.

Greenberg said that if further measures were needed to ensure clubs abide by the concussion rules they would be introduced.

“Rugby league led the way in implementing a policy to deal with head knocks and concussion last year and the initial club support was encouraging,” Greenberg said.

“We are determined to maintain our leadership position in this area because we have a duty to protect our players.

“The last thing anyone wants to see is players put at risk by being sent back on the field when they should be taken out of the game, assessed and treated.

“So, if we need to change our policy relating to concussion to make it stronger then that is what we will do.”

Greenberg said the NRL would complete its investigations into several incidents before commenting any further.