A sumo grand champion may face a police probe into the alleged assault of a junior wrestler, authorities said Wednesday, as more details emerged of a scandal that has rocked Japan's national sport.

Mongolian yokozuna (grand champion) Harumafuji is alleged to have smashed a beer bottle over a fellow wrestler's head and hit him repeatedly after the younger man pulled out his smartphone while he was speaking to him.

Headlines screaming "arrest" and "retirement" were splashed over the front pages in the sumo-obsessed country, as the 33-year-old is likely to have to step down from his lofty position if charged.

A spokesman for the sumo association told AFP that a police report had been filed on behalf of the 27-year-old assaulted wrestler -- Takanoiwa, also from Mongolia -- by the fighter's team.

The sumo association has set up a committee to investigate the issue but declined to comment further "until we find out the truth about the incident", he said.

Police could not confirm they have received the report, but said: "It would be true if the victim's side said so."

"Generally speaking, police start probing the case when we receive a report," said a spokesman, who declined to give his name.

The alleged assault took place last month when Mongolian wrestlers were relaxing over drinks after a tournament.

According to several media reports, Harumafuji flew into a rage when Takanoiwa tried to take out his phone to take a call during a conversation.

Kyokushuzan, a former Mongolian sumo wrestler who heard details from people who were at the scene, told private broadcaster TBS: "When I heard about it, I thought to myself 'this is awful.'"

"A yokozuna is like a God and it is not good if such a person gets drunk and hits someone," he said.

According to the Mainichi Shimbun, which cited several unnamed sources, the angry Harumafuji beat the younger wrestler with his hands repeatedly even after a bleeding Takanoiwa collapsed, chastising him for not paying attention while he was speaking.

About 10 sumo wrestlers, including two other Mongolian grand champions and Japanese wrestlers were at the drinking session, the report said.

The ancient sport has an extremely strict protocol, and yokozuna are expected to be beyond moral reproach in addition to showing superior strength and technique in the ring.

Daichi Suzuki, chief of the Japan Sports Agency, told reporters Tuesday that his agency was conducting hearings on the incident.

"We are absolutely against violence and we must eradicate it," he said.

The affair even reached the top levels of government, with the chief cabinet secretary taking questions on it at his regular briefing.

"It's important to find out what actually happened," said Yoshihide Suga.

"Many people want wrestlers to do their utmost in training ... and behave with the long history (of the sport) in mind," he told reporters.