Yokozuna Kisenosato, who came from behind to win the Spring Grand Sumo Tournament on Sunday despite injury, was diagnosed with muscle damage in his left upper arm and needs one month of treatment, a Japan Sumo Association source said Wednesday.

Kisenosato, who also won the previous tourney in January and became the first Japan-born wrestler to be promoted to sumo's highest rank in 19 years, will miss the spring regional sumo tour scheduled to begin this coming Sunday.

The 30-year-old may join the monthlong tour midway through, but will concentrate on treating his injury for the time being, the source said.

His stablemaster, Tagonoura, said Kisenosato's medical certificate has been presented to the sumo association. "I'm sure he wants to appear (in the regional tour), but we must first make sure he is fully healed," Tagonoura said.

Kisenosato sustained the injury on Friday when he was tossed off the ring by Mongolian yokozuna Harumafuji and fell to his first loss on the 13th day of the 15-day meet in Osaka.

He continued to compete, defeating Terunofuji on Sunday to take the championship to a playoff, where he beat the Mongolian ozeki again to win his second straight sumo title.