Responding to leaked documents that apparently bear Mr Gregg's signature and indicate he authorised a suspect payment to a United Arab Emirates firm, Primary Health Care told the ASX on Friday that it knew he was participating in an investigation by Australia's corporate watchdog.

"The board of Primary has been updated on the status of the ASIC investigation by Mr Gregg, insofar as the investigation involves Mr Gregg, and has been assured that Mr Gregg has fulfilled and continues to fulfil all of his obligations in respect of the investigation, and also that in his position with Leighton Holdings, Mr Gregg acted at all times in accordance with the law," the company said in a statement to the ASX.

Primary did not use the statement to guarantee Mr Gregg would retain the role of chief executive, but said; "The board remains comfortable with the performance and conduct of Mr Gregg since he was appointed chief executive of Primary."

Mr Gregg is one of several corporate figures to be caught up in a corruption and bribery investigation that centres on a Monaco-based company that worked as a fixer for energy and energy services companies to win contracts in middle eastern countries.

Another Australian company has been forced into a statement over the affair on Friday morning, with Worley Parsons telling the ASX it had no relationship with the Monaco-based company Unaoil.

But Worley confirmed Fairfax Media reports that it had engaged an agent to help it win oilfield contracts in Kazakhstan around 2008.

Fairfax reported that a middleman, Stefano Borghi, helped Worley gain inside information about the awarding of contracts on the Kazakhstan oilfield.

Worley told the ASX on Friday that Mr Borghi was a representative of the agency it had employed, and that both the agency and Mr Borghi were bound to agreements to act ethically during the term of the agreement.

"Our association with Stefano Borghi was as a representative of the agent, and so he was also bound by these processes and this commitment," it said.