Police are set to refer grand champion Harumafuji to prosecutors by the end of the year on suspicion of assaulting lower-ranked sumo wrestler Takanoiwa in a drunken brawl, investigative sources said Tuesday.

Under questioning late last week, the 33-year-old Mongolian yokozuna has admitted to striking 27-year-old Takanoiwa with his palms, his fists and a karaoke machine remote control, according to the sources.

Takanoiwa is believed to have suffered head injuries after being struck with an object, but Harumafuji has denied allegations that he hit the fellow Mongolian with a beer bottle in the late-October incident at a restaurant-bar in the western Japan city of Tottori, the sources said.

The police have determined that they can continue the investigation without arresting Harumafuji as there is no fear of him fleeing or destroying evidence, the sources said.

The police are carefully looking into how Harumafuji injured Takanoiwa but it remains unclear how accurately Takanoiwa can recall the incident as the No. 8 ranked maegashira has told police he kept his eyes closed as he was being hit.

According to other sources close to the matter, Harumafuji was angered by Takanoiwa trying to use his smartphone while being scolded for his behavior by yokozuna Hakuho, who was also present.

Mongolian yokozuna Kakuryu, sekiwake Terunofuji and some Japanese wrestlers were among the group drinking with the three in a private room in the restaurant-bar, the sources said.

The police are soon expected to question Kakuryu and Hakuho among others.

Sumo fans were disappointed by the news reports that Harumafuji was expected to be referred to prosecutors for the assault charge. Miyu Suzuki, 26, who attended the ongoing Kyushu Grand Sumo Tournament from Osaka said, "Sumo was finally regaining popularity, so it is sad that it has been taken up by media almost daily in such a way."

Takanoiwa has missed the tournament after being diagnosed with head injuries including a suspected fracture at the base of his skull and cerebrospinal fluid leak.

Harumafuji also withdrew from the tournament on the third day after the media reported the scandal.

The Japan Sumo Association has said its crisis management panel will investigate the case and hand down a judgment or punishment sometime after the ongoing tournament ends on Nov. 26.