Sumo grand champion Harumafuji has said he will retire from the sport, in a scandal that has rocked Japan's highly ceremonial sport.
Harumafuji is being investigated for an alleged assault on a junior wrestler, with his palms, fists and a remote control, Japanese media said.
The 33-year old Mongolian has since apologised for "causing trouble".
Japan's sumo world has been hit by scandals involving violence, mafia links and match fixing in recent years.
Harumafuji started his career in Japan at the age of 16 and was promoted to grand champion or yokozuna - sumo's highest rank - in 2012.
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Harumafuji's apology came after local media reported he had beaten junior wrestler Takanoiwa during a drinking session with other wrestlers.
Takanoiwa had to be hospitalised after suffering a concussion and a fractured skull base in the incident, local media reported.
A spokesperson for Japan's Sumo Association (JSA) said Harumafuji's coach Isegahama had told the JSA on Wednesday of the wrestler's decision to quit.
Mongolian sumo wrestler yokozuna, or grand champion, Harumafuji (R) and stable master Isegahama (L) - 14 November 2017Image copyrightAFP
Image caption
Stable master Isegahama and his star wrestler Harumafuji
At a Monday press conference, a speaker for an advisory body to the JSA had said the case required "extremely harsh punishment" but that no final decision had been made yet.
"There is almost no doubting that an act of violence was carried out," he said.
What is sumo?
Japan's much-loved traditional sport dates back hundreds of years
Two wrestlers face off in an elevated circular ring and try to push each other to the ground or out of the ring
There are six tournaments each year in which each wrestler fights 15 bouts
Wrestlers, who traditionally go by one fighting name, are ranked and the ultimate goal is to become a yokozuna (grand champion)
Bullying and mafia-links
The incident follows a string of similar scandals and reports of violence.
In 2016, a wrestler and his coach had to pay nearly $300,000 (£230,000) to a fellow fighter they allegedly abused so badly he lost sight in one eye, according to reports.
Thirteen senior wrestlers were implicated in a match fixing scandal in 2011 while a year earlier, the sport was rocked by alleged links between sumo wrestlers and the mafia-like yakuza crime syndicates.
Another Mongolian grand champion retired from the sport in 2010 after reports of his involvement in a drunken brawl.
In 2007, a teenage novice died after he was beaten up by older wrestlers in a case exposing a culture of bullying and hazing within the traditional sport's strict hierarchy.