PARIS — A Tokyo court approved a 10-day extension of jail time for Carlos Ghosn, the head of the Renault-Nissan alliance, on Friday as prosecutors assess allegations of financial misconduct. An ocean away, the corporate titan’s problems were on show at the Group of 20 summit meeting: President Emmanuel Macron of France, where Renault is based, met with Japan’s prime minister to discuss the alliance.

Mr. Ghosn, a charismatic leader in the auto industry, is being investigated after a whistle-blower within Nissan, the Japanese automaker, alleged he vastly understated his compensation on securities filings. He has been in detention since Nov. 19, when he was arrested on his private jet soon after landing at Tokyo’s Haneda Airport.

Mr. Ghosn, who forged the alliance as a groundbreaking industry model for sharing technology and cost savings, has yet to be charged. But the Nissan board voted unanimously to fire him as chairman last week. Mitsubishi Motors, a Japanese automaker that joined the alliance in 2016, removed him as its chairman on Monday.

Greg Kelly, Mr. Ghosn’s former chief of staff and a Nissan board member, who was arrested at the same time, will also be detained for 10 more days. A former head of human resources and an American, Mr. Kelly has been described by the company as a “mastermind” of the alleged financial wrongdoing. Both men were in Tokyo for a board meeting.