The NRL has admitted it hired a forensic accountancy firm linked to commissioner Tony McGrath to investigate alleged salary cap breaches at Manly and Parramatta, raising serious questions about a conflict of interest.

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.

Warned off Manly: Those close to new Knights signing Mitchell Pearce had steered him clear of the Sea Eagles. Credit:Jonathan Carroll

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.