Momota was found to have COVID-19 after taking a mandatory test at Narita Airport in Tokyo, from where he was due to Bangkok today.

The Nippon Badminton Association withdrew its whole team from the Yonex Thailand Open and Toyota Thailand Open in response.

China had already announced that it will not send players to the events, leaving the nation's participation in the BWF World Tour Finals - currently scheduled for January 27 to 31 in Bangkok - in serious doubt.

The same is now true of Japanese players.

All three competitions are set to be held in Bangkok to end the coronavirus-impacted 2020 season, with the Yonex Thailand Open set to take place from January 12 to 17, followed by the Toyota Thailand Open from January 19 to 24.

The BWF and the Badminton Association of Thailand will invite replacement players and pairs, who are already scheduled to enter the "Asian Leg Bubble" in Thailand by tomorrow, to fill the tournament berths vacated by the Japanese players.

All three tournaments will go ahead as planned, the BWF insists.

Japan's withdrawal is a blow for organisers, especially given the nation topped the medals table at the 2019 BWF World Championships.

In addition to Momota's world title, Mayu Matsumoto and Wakana Nagahara won the women's doubles crown.

Nozomi Okuhara was women's singles runner-up and the nation won six medals across the tournament's five categories.

With five medals in total, China finished second in the medals table.

Momota was set to return to international competition after almost a year out, following rehabilitation from facial surgery and the pause caused by the coronavirus pandemic.

After the Malaysia Masters in January 2020, Momota was a passenger in a road-traffic collision.

The driver of the van the men's singles world number one was in died.

Momota suffered lacerations to his face and a broken eye socket.

Despite resuming training in late February, the COVID-19 pandemic led to the cancellation of countless competitions and the Japanese star also withdrew from the BWF Denmark Open last year due to concerns over the pandemic, meaning he went almost 12 months without tasting competitive action.

Momota won a national title last month on his return to competitive action and remains one of the favourites for Olympic gold at Tokyo 2020, having missed Rio 2016 through suspension following a gambling scandal.

There is increasing concern over the coronavirus infection rate in Tokyo, host city of the next Olympics and Paralympics.

Governor Yuriko Koike, along with counterparts from three neighbouring prefectures, yesterday asked that the Japanese Government declare a state of emergency.