Grand champions Hakuho and Kakuryu will both miss the Autumn Grand Sumo Tournament starting this weekend after deciding to pull out Friday due to injury concerns.

The 15-day tournament, which opens Sunday at Tokyo's Ryogoku Kokugikan, will be the first in 37 years to commence without any wrestlers occupying the sport's highest rank.

Undated combined photo shows Mongolian grand champions Kakuryu (L) and Hakuho. (Kyodo)

Both Mongolian-born yokozuna withdrew from the previous grand tournament in July. An injured knee forced Hakuho out with three days remaining, while Kakuryu forfeited his second-day bout with an elbow injury and did not return.

With the two 35-year-old grand champions out of the running, Asanoyama and Takakeisho, the two wrestlers at the sport's second-highest rank of ozeki, will be the men to beat.

The injury withdrawal is Kakuryu's fifth and Hakuho's fourth from the six grand tournaments over the past year.

Kakuryu's Michinoku stablemaster, the former ozeki Kirishima, indicated the yokozuna would consider retiring if he is unable to make a healthy return to competition.

"We've reached a stage where the question of retirement cannot be avoided," the stablemaster said Friday.

All-time championship record-holder Hakuho last completed a full tournament in Osaka in March, when he captured his 44th Emperor's Cup.

He underwent endoscopic surgery to repair his right knee on Aug. 13, but has not recovered enough to take part in the upcoming meet, according to his Miyagino stablemaster, the former maegashira Chikubayama.

"He wanted to compete, but hasn't healed enough. He's disappointed," he said.