Kyodo News
Image copyright Getty Images Image caption Shigeru Ishiba has asked for support from people to keep his mayoral duties
The Tokyo governor was taken to hospital as he recovered from taking a fall after returning from a holiday.
His doctor told reporters it is still too early to know if his condition is linked to fatigue.
It is the second time Shigeru Ishiba has been taken to hospital in two months.
He is unable to attend the city’s annual afternoon-long “Takai” celebrations on Sunday, its traditional time of year.
In early January he collapsed during an appearance in the reception area of a Tokyo hospital, telling journalists: “You never know when you will fall sick or need to go to hospital”.
His doctor told reporters the treatment he was receiving was being “put to good use”.
The mayor, who has not been the healthiest of public figures, has also undergone medical checks in previous years to check his blood pressure and weight.
In October he was reported to have been diagnosed with arthritis as part of a national health check after a painful fall on a crowded street.
The politician has attempted to take a largely hands-off approach to the preparations for hosting the 2020 Olympics and is now expected to withdraw from the running, his popularity in tatters, according to local media.
The Japanese Prime Minister has said the hospitalisation will not affect the city’s Games preparations.
