Preparing to defend his men's singles crown on home ice at the ISU World Figure Skating Championships, Japan's Shoma Uno was hardly brimming with confidence Tuesday.

The 25-year-old Beijing Winter Olympic bronze medalist expressed frustration after struggling with a number of his planned jumps in official practice ahead of the four-day championships opening Wednesday at Saitama Super Arena near Tokyo, which last hosted the event in 2019.

Japan's Shoma Uno practices ahead of the ISU Figure Skating World Championships at Saitama Super Arena in Saitama, near Tokyo, on March 21, 2023. (Kyodo)

Uno, who has won all four of his competitions so far this season, including a maiden Grand Prix Final and fifth national championship, described Tuesday's practice as his "worst of the season."

"I haven't been able to visualize my jumps," Uno said. "I need a big change if things are to improve."

The reigning champion nevertheless said he was determined to set things right by Thursday's short program when he will take on a field that includes Japan's Grand Prix Final runner-up Sota Yamamoto and 18-year-old American "Quad God" Ilia Malinin.

"Giving up is not an option," Uno said.

With skaters from Russia still under sanction in response to the country's invasion of Ukraine, Japan's defending women's world champion and Olympic bronze medalist Kaori Sakamoto could face her stiffest competition from compatriot Mai Mihara, winner of December's Grand Prix Final.

Last year's world silver medalist, Loena Hendrickx of Belgium, will also look to challenge the Japanese women starting with Wednesday's short program.

In pairs, Japan's 2022 world championship silver medalists Riku Miura and Ryuichi Kihara will renew their rivalry with title holders Alexa Knierim and Brandon Frazier of the United States.

The Japanese duo narrowly beat the Americans at the Grand Prix Final in Turin before going on to also claim the Four Continents Championship, which Knierim and Frazier skipped.

Japan's Kaori Sakamoto prepares for the ISU Figure Skating World Championships at Saitama Super Arena in Saitama, near Tokyo, on March 20, 2023. (Kyodo)