As tension between the NRL and the Sea Eagles intensifies over the way the investigation has been handled, head office has also denied former Roosters halfback Mitchell Pearce was "tipped up" about the impending breach notices, persuading him to steer clear of Manly and instead sign with Newcastle.

McGrath, who did not return calls, has been a commissioner since 2014.

His company, McGrathNicol, provides a range of financial services, including "successful preventative and responsive solutions to manage investigations, disputes, contracts, technology and commercial irregularities and obligations", according to his company's website.

In a stunning admission, the NRL confirmed McGrath's firm was contracted during last year's probe into the Eels, which unearthed almost $3 million worth of breaches over five years and resulted in the club being stripped of its 12 competition points, fined $1m and forced to shed players.

Asked if McGrath's firm had been used, an NRL spokesman said: "Yes, they are one of the leading forensic accountant firms in the country. They did the forensic work on the Parramatta salary cap investigation and did a professional, competent job so they were engaged for the Manly work as well. Mr McGrath was not involved in their appointment."

McGrath said, through the NRL, on Wednesday night that he retired as a partner of the firm about two years ago, but still does occasional consultancy work.

While there is no suggestion of wrongdoing of McGrath's behalf, the decision from the NRL's integrity unit to contract a company linked to a current commissioner will shock many stakeholders in the game, no matter how proficient it might be in uncovering alleged breaches of the salary cap.

The revelation comes as Manly starts to dig in over the NRL's preliminary findings into their alleged cheating over a five-year period.

Club officials had no comment on Wednesday night, but it is understood they are gearing up for a legal stoush, claiming there has been nothing more than procedural breaches of third-party agreements instead of systematic rorting.

Manly are increasingly bemused at comparisons to the Parramatta situation, which resulted in criminal charges after it was found, among other indiscretions, that invoices between the club and players were inflated in order to cheat.

The Sea Eagles are also unhappy at what they believe has been a drip-feed of information about the investigation to the media - something the NRL strongly denies.

That includes claims that Pearce was told in advance about the possible sanctions Manly faced, which warned him off signing with the Sea Eagles.

Mitchell Pearce was strongly linked to the Sea Eagles after the Roosters signed Cooper Cronk, and even more so after he asked for a release from the club. He has a close relationship with Manly coach Trent Barrett.

In the end, he signed with the Knights on a deal worth about $300,000 more per season than Manly were prepared to offer him.

"No player or club official was given any prior information about the preliminary findings or sanctions before they were released on Monday," the spokesman said. "In fact, no information leaked about the Manly investigation during the entire period of the inquiry."

Those close to Pearce ??? including those at the Roosters ??? had warned Pearce about the impending storm at the Sea Eagles over their salary cap.

Pearce's manager, Steve Gillis, said: "I can only speak on my behalf, but I had no discussion with the NRL about Manly's situation."