Japan fly-half Takuya Yamasawa has tested positive for Covid-19 and will miss Saturday's first test match against France, Japan's Rugby Football Union said on Friday.
Yamasawa's positive antigen test makes him the fourth player ruled out over a coronavirus infection. Seungshin Lee will take his place, with Shane Gates coming into the squad as a replacement.
The 27-year-old Yamasawa was sidelined a day after the Brave Blossoms said scrum-half Naoto Saito, hooker Shota Horie and full-back Ryuji Noguchi were all out because of Covid-19.
Local media reported fears that there could still be further cases in the squad, whose head coach has already acknowledged they face a "massive challenge" in Saturday's match against Les Bleus.
Temperatures are forecast to soar to 35 degrees Celsius by kick-off time in steamy Toyota, but coach Jamie Joseph said while his players will find the heat tough, France "will find it even more challenging".
"We've got to keep the game as fast as possible and back our ability to handle the heat a little bit better," he said Thursday.
Covid-19 disruptions mean the 2019 World Cup hosts have played only eight test matches since reaching the quarterfinals on home soil two-and-a-half years ago.