He drew parallels with the 1984 Games in Los Angeles in which there were concerns "about how many Olympic athletes were going to die because of the smog," and a Zika virus outbreak prior to the 2016 Games in Rio de Janeiro.
Organisers were set to allow 20,000 fans into the May 9 meet, according to Kyodo news agency, but tougher restrictions imposed by the Tokyo city government this month have forced a rethink.