Primary Health Care chief executive Peter Gregg will sue Fairfax Media for defamation following reports linking Mr Gregg to widespread corruption and graft in the oil industry.

Fairfax Media's The Age, and The Sydney Morning Herald, on Thursday published revelations implicating Australian companies including Worley Parsons and Leighton Holdings in the global scandal centred on Monaco-based oil company Unaoil.

Former Primary Health Care chief executive Peter Gregg. Credit:Daniel Munoz

The investigations also revealed that Mr Gregg is the subject of an active criminal investigation by the Australian Securities and Investments Commissions over a suspect $15 million offshore payment authorised while Mr Gregg was chief financial officer of Leighton Holdings.

Mr Gregg on Friday announced his intention to commence legal action against Fairfax Media, also owner of AFR Weekend.