The recent controversy over the "Japanese only" banner put up by Urawa Reds soccer fans is yet further testimony to the nation's entrenched insensitivity to racism and threatens Tokyo's credibility as host of the 2020 Olympics, experts said Friday.

The banner, written in English, was raised during the Saitama team's March 8 match against Sagan Tosu.

A deluge of protests followed, prompting the J. League to announce Thursday that Urawa's March 23 match against Shimizu S-Pulse will be played in an empty stadium, in what is one of the toughest penalties ever slapped on a soccer team in Japan.