One of the biggest stars of sumo wrestling is to announce his retirement on Wednesday, following allegations that he assaulted a fellow wrestler, as the reputation of Japan’s ancient sport is mired in yet another scandal.

Harumafuji, one of four reigning grand champions – or yokozuna – has told sumo authorities of his intention to quit, according to local media reports, weeks after he allegedly attacked a younger wrestler, leaving him with a fractured skull and concussion.

The dramatic manner of the Mongolian wrestler’s exit from sumo at the pinnacle of his career comes as the sport was beginning to regain its popular appeal after a slew of bad publicity.

The episode has prompted criticism of sumo authorities for failing to rid the sport of violence, a decade after a teenage trainee collapsed and died after being beaten by fellow wrestlers for threatening to abscond from his stable.

Violence aside, sumo has been rocked by evidence of match-fixing and illegal betting in recent years.

In 2010, another Mongolia-born grand champion, Asashoryu, was forced to retire, weeks after he allegedly assaulted a man outside a nightclub in Tokyo.

Harumafuji’s stable master Isegahama said the 33-year-old wrestler had “caused great trouble” to the sumo association and the watching public, adding that as a yokozuna he had to take responsibility for his actions.

He allegedly assaulted Takanoiwa, a lower-ranked wrestler from another stable, during an alcohol-fuelled evening at a restaurant in late October.

Initial reports alleged Harumafuji was armed with a beer bottle but several witnesses have since claimed that he repeatedly punched his victim, a fellow Mongolian, and struck him with the remote-controller for a karaoke machine.

He had reportedly turned on the 27-year-old Takanoiwa because the latter continued to look at his smartphone while he was being reprimanded for his poor attitude.

The injured wrestler did not take part in the recent 15-day tournament in south-west Japan, while Harumafuji withdrew on the third day after media first reported the assault allegations.

Police have questioned Harumafuji, who could be charged over the allegations, according to Kyodo news.

“Tremendous damage has been caused to sumo,” said Masato Kitamura, chairman of the body that rules on promotions to the sport’s highest rank, adding that the incident had “let fans down”.

Japanese media were unanimous in condemning Harumafuji and sumo authorities, warning fans could lose interest in the sport.