The Six Nations announced on Wednesday plans for an eight-team tournament to replace the cancelled November Tests.
Sources have told AFP 2019 Rugby World Cup hosts Japan as well as Fiji are set to join the Six Nations in two pools of four sides before a final play-off round in December.
"We are currently finalising match schedules, operational details including venues as well as commercial arrangements. Further announcements relating to this competition are expected to be made later this month," a statement said.
The southern hemisphere sides of World Cup winners South Africa, New Zealand, Australia and Argentina are unable to travel north due to the coronavirus pandemic.
According to reports they are expected to contest a rescheduled Rugby Championship in December with all games set to be played in New Zealand.