Police on Monday referred former sumo grand champion Harumafuji to prosecutors for his assault of a lower-ranked wrestler with prosecutors considering an indictment by the end of the year, sources close to the matter said Monday.

Prosecutors are expected to seek a summary indictment for a fine on the 33-year-old former yokozuna who put an end to his 17-year sumo career on Nov. 29 just weeks after the scandal surfaced, the sources said.

Investigative sources said police in Tottori Prefecture, where the assault occurred, are likely to have sent the case to prosecutors with a recommendation that he should be indicted.

The Japan Sumo Association has also investigated the incident and is expected to receive a final report on Dec. 20 from a crisis management panel that probed the case.

Japan Sumo Association Chairman Hakkaku said, "We will fully cooperate with prosecutors so that an impartial investigation and punishment will result while making full efforts to establish measures so that something like this does not happen again."

According to investigative sources, the then grand champion allegedly beat fellow Mongolian wrestler Takanoiwa, 27, with his palms and a karaoke machine remote control during a drinking session that lasted from the night of Oct. 25 into the early hours of Oct. 26 at a bar in Tottori. The wrestlers were in the area on a regional tour.

Takanoiwa suffered head wounds that required about 10 days to heal and filed a police report on Oct. 29. He was diagnosed at a hospital in Fukuoka with a suspected fracture at the base of his skull, among other injuries.

Harumafuji admitted to the assault during police questioning conducted on a voluntary basis, according to the sources. His lawyers released Monday a statement on behalf of the former champion, offering "heartfelt apologies to Takanoiwa and others."

The lawyers also said they will ask for a meeting with Takanoiwa and his stablemaster Takanohana to apologize for the assault and discuss compensation.

The investigative sources said Harumafuji is believed to have been angered by Takanoiwa's inattention while Mongolian yokozuna Hakuho was giving him advice.

Speaking at a press conference upon his retirement, Harumafuji said he had been trying to fulfill his outside-the-ring duty to teach his fellow Mongolian wrestler manners, but ended up "hurting" Takanoiwa and "caused a stir."

According to a Japan Sumo Association investigation, the assault occurred after Hakuho told Takanoiwa not to forget the kindness he received during his high school days. Takanoiwa was looking at his smartphone at the time and replied, "It's an email from my girlfriend."

"I can only hope this kind of incident will never happen again. We will try to regain public trust by showing our best performance in the ring and keep dedicating ourselves to our duties," Hakuho told reporters on Monday.

Harumafuji's retirement was seen by many Japanese as inevitable as he had failed to live up to the high standards of dignity that any yokozuna in Japan's ancient sport is expected to show. But some sumo fans in Japan, and others who know the wrestler well, expressed disappointment over his premature exit from the sport.

After making his professional debut in 2001 under the ring name Ama, Harumafuji, whose real name is Davaanyam Byambadorj, was promoted to yokozuna in 2012 and won nine titles.

The scandal dealt a blow to the sumo world which was already tainted by cases of match-fixing, violence and bullying.

In 2010, then grand champion Asashoryu, another Mongolian, allegedly seriously injured a male acquaintance in a drunken rampage. He also announced his retirement soon afterward.