Ex-Nissan chief Carlos Ghosn has been suffering from a high fever and was unable to meet investigators for questioning on Thursday, local media said, citing his lawyers.
The 64-year-old auto tycoon, who emerged in public on Tuesday for the first time since his November arrest, has been ill since Wednesday night and needed some time to rest, according to several local news outlets.
His lawyer was not available for immediate comment.
According to the Nikkei daily, a doctor who examined him said Ghosn "required rest and was unfit for interviews (by prosecutors) and meetings (with his lawyers and consular visitors)".
At a dramatic court appearance on Tuesday, Ghosn appeared to have lost a lot of weight in detention but otherwise seemed in good health, fiercely denying the allegations against him in a strong voice.
Nevertheless, he did cough occasionally during the proceedings that lasted almost two hours.
The once-revered former Nissan chairman has now languished in a Tokyo detention centre for more than 50 days as he fights multiple allegations of financial misconduct.
He has been formally charged with under-declaring his income by tens of millions of dollars in an apparent bid to avoid accusations he was overpaid.
He also faces questioning in connection with alleged attempts to transfer personal investment losses to Nissan and making unnecessary payments to a Saudi associate from company funds.
His detention period over this latter allegation ends on Friday but his lead lawyer has expressed doubts that he could win bail, saying he expected Ghosn to stay in pre-trial detention for up to six months.
The Tokyo District Court has denied his lawyers' requests to end his detention, saying he presents a flight risk and could tamper with evidence.
Ghosn denies all the allegations against him, saying he had been "wrongly accused and unfairly detained based on meritless and unsubstantiated accusations".