Watch: 'A few more kilos': Djokovic comes up short... at sumo

Tokyo: World number one Novak Djokovic might be top seed at the Japan Open starting Monday, but when he took to the ring for a sumo bout in Tokyo, he came up short.

"I felt that I am out of shape (for sumo) a little bit," he told the ATP tour website after trying his hand at the sport on Monday, hours before his first match.

With his teeth gritted and his fingers sinking into the giant arm of his opponent, Djokovic tried and failed to move a wrestler a few inches inside a dohyo, or sumo ring.

"I think with a few more kilos, I'll be ready to compete," he joked. "Probably three times as much as I have right now would be the right measurement for me to compete."

The ancient sport of sumo is a big draw for foreign visitors to Japan, with new spectators often surprised by the agility of the enormous participants.

"It's quite impressive to see also how flexible they are," Djokovic said.

"I didn't think that they were that flexible considering it's a heavyweight sport, but I see that they are paying a lot of attention to the mobility of their joints and the flexibility, which is of course what allows them to move around as agile as possible at their weight."

Djokovic said he was no stranger to the sport though, having watched it with his father in the past when they cheered for Akebono - who reached the yokozuna status that is the pinnacle of sumo.

Djokovic took to the court for the first time on Monday for a doubles match with countryman Filip Kraijinovic.

The Serbian duo were bested by Croatia's Mate Pavic and Brazil's Bruno Soares 6-2, 4-6, 10-4.