Former Nissan boss Carlos Ghosn will "vigorously" defend himself in a Japanese court this week after refusing to sign a confession in return for being released from custody, his son has told a French Sunday newspaper.

The auto tycoon who has been held since his shock arrest in November on allegations of financial misconduct is due to appear in a Japanese court on Tuesday to hear the reasons for his detention.

He will give his version of events for the first time, his son Anthony told the French weekly newspaper Le Journal du Dimanche (JDD).

The father-of-four has gone from heading a powerful international auto alliance to languishing in a Tokyo detention centre, where his stay has been repeatedly extended.

Anthony told the JDD that his father would be released if he signed a confession.

He can "tell the prosecutor that he is contesting the charges or instead he could confess and be released. For seven weeks his decision has been quite clear," he said.

"The paradox is that the confession he has been asked to sign is written only in Japanese," adding that his father does not understand it.

He added that the defence do not yet have a complete file on the case.

Stunning reversal of fortune

Authorities are pursuing three separate lines of enquiry against the 64-year-old Franco-Lebanese-Brazilian executive, involving alleged financial wrongdoing during his tenure as Nissan chief.

They suspect he conspired with his right-hand man, US executive Greg Kelly, to hide away around half of his income (some five billion yen or $44 million) over five fiscal years from 2010.

They also allege he under-reported his salary to the tune of four billion yen over the next three fiscal years - apparently to avoid criticism that his pay was too high.

The growing case against the auto tycoon represents a stunning reversal of fortune for a man once revered in Japan and beyond for his ability to turn around automakers, including Nissan.

"He is ready to defend himself vigorously and is very focused on the goal of responding to the accusations against him. He is particularly calm," said Anthony, who has not spoken directly with his father.

"For the first time he will be able to explain all the charges against him and give his version and I think everyone will be quite surprised to hear his version of the story."

Ghosn will appear handcuffed in prison clothes and will have 10 minutes to speak, his son said.

He has lost ten kilos since his detention began due to a prison diet of three bowls of rice a day, and spends his time reading books.

"He takes all this as a challenge," Anthony added.

Prosecutors have pressed formal charges over the first allegation -- that Ghosn under-reported his salary between 2010-2015 -- but not yet over the other accusations.