Senior executives at Renault-Nissan worked on a plan as far back as 2010 to pay Chairman Carlos Ghosn part of his salary without having to publicly disclose the amount, according to an email seen by CNBC.

In the text, Ghosn's alleged accomplice and former Nissan Director Greg Kelly asked Renault's then general secretary, Mouna Sepehri, to weigh up the legal risks of such an action. Sepehri is now executive vice president at Renault and a permanent member of the Renault-Nissan Alliance Board.

The email, dated April 2010, outlines a scenario where Ghosn could receive payment through the Dutch holding firm, RNBV, which was jointly owned by the French and Japanese carmakers. Within the text, Kelly stated that he had warned Ghosn of "some legal risk" to this approach but wanted further legal opinion from other executives, including Sepehri.

Kelly wrote: "I greatly appreciate the work you have done to analyze whether part of the CEO's compensation can be paid without disclosing it publicly." In a Reuters report Wednesday, that CNBC can confirm, that 2010 plan was never put into action.

Renault was not immediately available for comment when contacted by CNBC, but told Reuters that Kelly had "consulted several people at Renault and Nissan to establish whether it was legally possible that part of the CEO's compensation be paid by RNBV to reflect the time he spent working on alliance synergies."

Ghosn and Kelly are currently in a Tokyo jail following allegations from Japanese prosecutors that the pair failed to declare around $43 million in deferred compensation between the years of 2010 and 2015.

The exclusive report by Reuters on Wednesday also says bankers at Renault-Nissan developed plans to funnel millions of euros in bonus payments to Ghosn and other senior managers through a Dutch company.

Ghosn, via his Japanese lawyer, has denied any wrongdoing. Kelly also denies any wrongdoing and the pair have had little opportunity to respond to the allegations.

In a statement to CNBC, Nissan said: "We cannot comment regarding the specifics of this investigation and other reports."