WBO world super flyweight champion Kazuto Ioka had tested positive for doping in December when he defended the title for the second time, sources familiar with the matter said Monday.
Ioka's private attorney Masanao Hattori said the 32-year-old, who tested positive for cannabis, has never taken illegal or illicit drugs.
The Japan Boxing Commission consulted with the police after its mandatory test came back positive.
Hattori admitted a voluntary questioning of Ioka has taken place, and said in a statement, "I heard the investigation is concluded and understand that he is cleared of the charge."
The JBC said it will release a statement in the coming days.
Ioka in 2019 became the first Japanese male boxer to conquer four divisions.
He defended his WBO world super flyweight belt on New Year's Eve by beating his Japanese compatriot and previously unbeaten top-ranked challenger Kosei Tanaka in an eighth-round technical knockout.
Ioka was disciplined by the JBC in January after tattoos on his left arm became visible during the match.