Six Australian National Rugby League (NRL) clubs Tuesday admitted they were mentioned in a nationwide sports doping scandal, and vowed to support any investigations.

North Queensland, Penrith, Canberra, Newcastle, Manly and Cronulla all said they had been contacted by NRL chiefs after the Australian Crime Commission granted the league permission to notify any clubs it mentioned in its report.

The official report, released in summary last week, said use of prohibited substances including peptides, hormones and illicit drugs was common across multiple sporting codes, sending shockwaves through Australia.

Australian Rules football has already admitted at least one of its clubs and one player from another club had been implicated.

Cricket, football and rugby union authorities have said they are not under investigation.

"Our club will cooperate with any official enquiry," Newcastle Knights chief executive Matt Gidley said, adding that the NRL contacted them on Monday but they had no further information or details on how they were involved.

"We maintain full confidence under the management of (coach) Wayne Bennett.

"Until we receive further information from the NRL and/or ASADA, there is nothing further we can add," he added, referring to the Australian Sports Anti-Doping Authority.

Reports said the 10 other NRL clubs all confirmed they were not mentioned in the report.

"As previously stated, we fully support any investigations by the NRL or the ACC in relations to these matters," said Canberra Raiders chief Don Furner.

"Our club will continue to work with the NRL and ACC until these matters are resolved and will update our members, sponsors and supporters when we can."

In the wake of the report, the NRL has committed to establishing a fully resourced integrity unit and appointed a former federal court judge to assist in its investigations.

NRL chief executive David Smith said the six teams would be briefed by ASADA later Tuesday on why they were being probed, but refused to go into details.

"These are complicated matters," he told a press conference.

"I'm not speculating on the investigation. The only thing I've been allowed to do is tell clubs involved that they've been referred to.

"What I can say... is that the vast majority of our players and team officials do the right thing."

The ACC report did not name specific players, teams or codes, citing legal reasons, sparking concern that all sportspeople and those working with them had been tarred with the same brush.

World Anti-Doping Agency chief John Fahey, an Australian and a keen rugby league fan, told Sydney's Daily Telegraph he did not understand why the government released the report in such a broadbrush way.

"Whatever is behind it all, we need to know. But to be told it in general terms, and have to wait significant time to see how big the problem is, is something I am simply puzzled by," he said.

"I do not understand the motive behind that or the strategy. What I am saying is that there may be a good reason but I can't find it at this stage."