Nihon University is questioning a professor emeritus who borrowed ¥20 million from a former senior member of the Yamaguchi-gumi yakuza syndicate, school officials said Tuesday.

The 77-year-old expert on international law has admitted borrowing the money and has not repaid it, a university spokesman said.

He said the professor and former gang member have been acquainted for more than 20 years. Their names have not been released.

The Tokyo-based private university, which at more than 66,000 students boasts the nation's largest enrollment, convened a meeting Tuesday of an in-house investigative committee comprised of lawyers.

Masamichi Ikemura, dean of the law faculty, told reporters Monday the university may fire the scholar.

"It is very regrettable that (the professor), as someone belonging to an educational institution, was friendly with anti-social forces," Ikemura said. "We will deal with the matter rigorously, and the option of dismissal will be on the table."

The scholar, whose gender was also not disclosed, retired as a professor in 2008, has been working as a part-time lecturer in the university's law school. In the wake of the scandal, the university canceled all of the teacher's classes and is now looking for a replacement.

"The professor has admitted to basic facts around the case, but does not think the loan itself was a bad thing," the university spokesman said. "It shows an enormous lack of seriousness about the issue."

According to court records, the professor emeritus borrowed the ¥20 million around 10 years ago to finance an overseas business. The loan surfaced in a civil suit involving financial trouble between the former yakuza and another person.

The professor appeared during a session of the Saitama District Court in August 2014 as a witness for the former yakuza member and referred to the ¥20 million loan as a transaction between "friends."