Japan have decided against taking part in this autumn's 'Eight Nations' tournament due to the coronavirus pandemic, sources told news agency AFP.
The host of last year's Rugby World Cup were set to join England, France, Ireland, Italy, Scotland and Wales, as well as fellow invitees Fiji, for the competition which is set to replace the cancelled November Tests.
Ireland were originally due to welcome their World Cup conquerors for the last of the November internationals, and could have faced Japan had the sides finished in the same position in their respective groups in the eight-team competition.
The BBC reported that Bill Sweeney, RFU CEO, is still hopeful that Japan will travel, however, he added that contingency plans were in place.
Georgia, often mooted as a contender for a Six Nations place, would be the obvious stand-ins should Japan decide not to travel to Europe.
The Brave Blossoms were to join France, Gregor Townsend's Scotland as well as Franco Smith's Italian side in a four-team group held between 14 November and 5 December.
The Asian country has recently limited foreign arrivals due to the Covid-19 outbreak which according to local media has hampered the return of some of Japan's coaching staff.
The measures restrict plans by Jamie Joseph, who led his outfit to the World Cup quarter-finals for the first time in 2019, to hold a training camp ahead of the newly-created competition.
Ireland are due to face Italy at home on 24 October before finishing their 2020 Guinness Six Nations campaign against France away a week later.