Ghosn, arrested and detained in Tokyo for about two months, has already been indicted on charges of under-reporting his income for eight years at Nissan through March 2018, and temporarily transferring personal investment losses to the automaker during the global financial crisis.
"That such misconduct also occurred at our affiliate is beyond shocking ... it's sad," Masuko told reporters, referring to the payments made to Ghosn from Nissan-Mitsubishi B.V., registered in the Netherlands in 2017.
According to Mitsubishi's legal team, over April-November 2018, Ghosn received around 5.8 million euros ($6.61 million) in annual pay for his role as managing director, a 1.4 million euro signing fee and an undisclosed incentive from the JV.
Ghosn's lawyer, Motonari Otsuru, could not be immediately reached by telephone for a comment on Friday. Ghosn has denied all previous charges against him.
The arrest of Ghosn, who spearheaded Nissan's turnaround two decades ago, and the list of charges against him have jolted the auto industry, while muddying the outlook for Nissan's three-way alliance with Mitsubishi and Renault.
Renault has come under a lot of pressure in recent days from its biggest shareholder, the French government, to replace Ghosn as its CEO and chairman. The automaker has kept him at its helm, even as Nissan and Mitsubishi moved swiftly to oust him as chairman after his arrest.
The French automaker, however, confirmed on Thursday that it was considering new leadership, after Finance Minister Bruno Le Maire called publicly for a board meeting to address his succession.
Ghosn's pay has been a hotly debated issue at Renault's shareholder meetings where he lost a vote on pay a few years ago. He has also been in news previously for hidden bonus plans.
Reuters reported in 2017 on a plan by Renault-Nissan bankers to pay millions in undisclosed bonuses via a specially created Dutch service company to Ghosn and other managers. The plan was scrapped after the Reuters report.