Greg Kelly, a former close colleague of Carlos Ghosn, said he was "shocked" at the flight from Japan of the ex-Nissan boss and worries it could hamper his own battle against financial misconduct charges.

The softly-spoken American, 63, gave a rare interview to AFP as he awaits trial in Tokyo, confiding his surprise at Ghosn's sudden escape to Lebanon and his fears that he will not receive a fair hearing.

"I was completely surprised. I had no idea that would happen," Kelly said. "I was shocked."

Like Ghosn, Kelly stands accused of conspiring to conceal from shareholders tens of millions of dollars in pay the former chief executive was promised after his retirement. Kelly faces up to 10 years in jail if convicted.

"And now he's not here. So, it really makes it to me seem quite difficult to really have a trial now that's going to be fair," he said.

"If the leading witness isn't there, how do you really try this case in a logical way?"

Often presented as a "right-hand man" or close adviser to Ghosn, Kelly said the two men were not personally close.

"I didn't even know he got married," he said of Ghosn's lavish wedding at the Palace of Versailles in 2016 that later attracted criticism.

"I met with Carlos Ghosn only twice a month. In terms of a personal relationship, that didn't occur. It was business issues," stressed Kelly, whose discreet style contrasts somewhat with his more brash former boss.

- 'Very, very painful' -

Kelly and Ghosn both arrived in Tokyo on the same fateful day in November 2018 and were arrested by Japanese authorities. They say Nissan lured them to the country on the pretext of an important board meeting.

Kelly was released on bail on Christmas Day after more than a month isolated in a detention centre -- especially uncomfortable as he was due to return to the United States for treatment on his back.

"Really, it was painful. Very, very painful," Kelly said, adding that he had tried to explain to wardens that he could not sit on the floor as required.

"I'm not the type of person that's going to bang on the door and yell and scream or anything like that."

Since his release, he has undergone surgery in Japan that seems to have worked, although he said he still suffers from numbness in his feet, arms and legs.

To keep fit and relieve stress, he has taken to jogging a popular five-kilometre (three-mile) route around the Imperial Palace in Tokyo, near the modest apartment he shares with his wife Donna.

- 'Lonely existence' -

Like Ghosn, Kelly strenuously denies any wrongdoing.

"I didn't do anything criminally wrong in Japan," he stresses, adding that the departure of Ghosn -- who faces more charges than Kelly -- might open a door to a resolution within the firm.

"For me, this could be resolved within Nissan. If it's an error about reporting something that was never agreed and never paid...," he said, tailing off and adding: "But you know, I'm caught in the system right now so..."

He still does not know when his trial will begin, despite another pre-trial session on Friday.

Kelly defers questions about the details of his planned defence to his lawyers. He spends most of his day going through mountains of electronic documents furnished by the Japanese prosecutors.

The couple say they miss their children and grandchildren in the United States but also their own friends at Nissan, whom they are banned from contacting while the case is ongoing. It is, says Kelly, a "lonely existence."

Photos of their loved ones adorn the walls of their Tokyo apartment but they have not set down roots there.

"This is not called home. This is called the apartment. You never say you're 'going home'. You say you're 'going back to the apartment'," said Donna Kelly.

She spends her days learning Japanese to sustain the student visa that allows her to stay with her husband.

"You can't miss school and you have to get the grades," she said.

Despite his predicament Kelly refuses to hold a grudge against Nissan, the company for which he worked "seven days a week" for nearly 30 years.

The Ghosn saga has battered trust in the firm and its most recent results showed a more than 87-percent plunge in net profit for the nine months to December.

"This thing that I'm caught up in, that doesn't make me want Nissan to do badly," Kelly said.

"I want Nissan to do well."