The Japan Sumo Association has acknowledged that it was wrong to allow a sumo wrestler to climb into the ring after he was diagnosed with influenza.
The association said the wrestler, Takagenji, felt unwell and went to a hospital on December 11, during a regional tour of Saga City in southwestern Japan.
Takagenji informed tour organizers of the diagnosis, but climbed into the ring later the same day.
The regional tour lasted from December 1 to 15, and many wrestlers were absent due to a flu outbreak.
The association's public affairs director, Shibatayama, admitted that the association failed to handle the matter properly.
The association says it will ensure that wrestlers and officials are isolated promptly if they are diagnosed with influenza.
The head of Japan's Sports Agency, Daichi Suzuki, questioned the association's handling of the matter. He said it is the norm for flu patients to be separated from others until their recovery.