Former Nissan boss Carlos Ghosn received nearly eight million euros in “improper payments” from a Netherlands-based joint venture, the Japanese car giant alleged on Friday, threatening to sue to recover the funds.

Nissan said Ghosn entered into a personal employment contract with Nissan-Mitsubishi BV (NMBV), a company formed “with the mission of exploring and promoting synergies within the Nissan-Mitsubishi Motors partnership”.

Under that contract, he received a total of 7,822,206.12 euros (including tax) in compensation and other payments of NMBV funds,” Nissan said, citing an ongoing investigation into alleged wrongdoing by Ghosn.

The firm said the contract was signed without consultation with current Nissan CEO Hiroto Saikawa or Mitsubishi Motors CEO Osamu Masuko.

“Nissan views the payments Ghosn received from NMBV to be the result of misconduct and will consider measures to recover from Ghosn the full sum,” the firm said in a statement.

Since his out-of-the-blue arrest on November 19, Ghosn has been kept in a Tokyo detention centre and has made only one public appearance in court when he passionately rejected the accusations against him.

Ghosn faces three formal charges. First, he is accused of under-declaring his income by five billion yen ($46 million) between 2010 and 2015 in official documents to shareholders, apparently to fend off criticism he was overpaid. Second, he stands accused of continuing this practice for three more years, understating his pay by a further four billion yen. A third, more complex, charge relates to allegations he sought to transfer personal investment losses to the firm and paid a Saudi intermediary from company funds to stump up collateral for him.

'Global Donation Advisory Council'

The 64-year-old auto tycoon rejects all the charges, arguing in court that he has been “wrongly accused and unfairly detained based on meritless and unsubstantiated accusations”.

He has appealed several times to be released on bail and filed another appeal earlier. So far, the appeals have all been rejected, with the court reasoning that he is a flight risk and could tamper with evidence.

His lawyers have vowed to lodge an appeal with the apex court against his continued detention, but even his lead attorney has told reporters it is unlikely he will taste freedom before a trial — and that could take six months at least.

Meanwhile, the allegations continue to stack up against Ghosn — once revered as a corporate genius who saved Nissan from the verge of bankruptcy. He is said to have had luxury houses in Beirut and Rio de Janeiro paid for by the company — plus costly renovations for the first property.

It is also alleged one of his sisters received $755,000 for work carried out between 2003 and 2016 as part of a “Global Donation Advisory Council” — a body which has never existed according to sources close to Nissan.

Nissan is thought to be looking into other payments such as donations to universities in Lebanon or a subscription to a yacht club in Brazil for $63,000.

Ghosn has been unable to defend himself against these new allegations and they do not form part of the formal charges against him. But the Japanese firm is ramping up its probe into its former leader and more revelations are likely as it continues.

Nissan has also been slapped with formal charges over the affair as they submitted the documents to shareholders that allegedly under-declared the executive's income.