TOKYO, Nov 14 -- Mongolian sumo grand champion Harumafuji on Tuesday apologised for injuring a fellow wrestler who media said suffered a fractured skull after being hit with a beer bottle in the latest scandal to engulf the closed, hierarchical sumo society.

Harumafuji, 33, hit Takanoiwa on the head last month at a party of sumo wrestlers from Mongolia, public broadcaster NHK quoted unnamed sources affiliated with the Japan Sumo Association as saying.

Takanoiwa, 27, is not taking part in the 15-day tournament that started on Sunday in Fukuoka, western Japan, due to the fracture, concussion and several other injuries, according to the association's Twitter entry.

Takanoiwa told the association it would take two weeks for the injuries to heal, NHK and other media said. The association said Harumafuji would sit out the tournament and that it was looking into the matter.

"As for Takanoiwa's injuries, I apologise deeply for causing trouble for stable master Takanohana, people affiliated with Takanohana stable, the Sumo Association and my stable master," NHK showed Harumafuji telling reporters.

He declined to give details of the assault, NHK said.

Takanoiwa belongs to a stable led by former grand champion Takanohana. The stable master has already reported the incident to police, Kyodo news agency said. It was not immediately clear if Harumafuji would be charged.

No one was available for comment at Harumafuji's or Takanoiwa's stable.

In 2010, former stable master Tokitsukaze was sentenced to fives years in prison for instructing seniors to beat up a novice 17-year-old wrestler.

The same year, grand champion Asashoryu, also from Mongolia, retired from the ancient sport following a probe into reports of a drunken scuffle in Tokyo.