World Cup champions South Africa and Japan could feature in an international 'festival of rugby' tournament alongside the Six Nations sides this autumn, under proposals being considered by the Rugby Football Union.
There is continued uncertainty over whether the autumn internationals will be able to be staged as planned due to the coronavirus pandemic, with officials drawing up a series of contingency plans.
England are scheduled to host New Zealand, Argentina, Tonga and Australia at Twickenham this November, but RFU chief executive Bill Sweeney says including "guest" countries in a one-off eight-team competition is one fall-back option.
"You take the Six Nations and you add in some guest teams," Sweeney told Sky Sports News.
"You could actually have some good fun with various different teams that you could incorporate in that and you create a real festival of rugby, a celebration of the values of rugby and returning to play rugby in autumn of this year.
"We are just going through all the various different scenarios and what we think makes most sense."
Sweeney confirmed on Thursday that one other option would see a 'home and away' Six Nations take place, split from a November start and finishing in its traditional March slot - but the preference is for England to play the original autumn schedule in front of a socially-distanced crowd at Twickenham.
"You would be surprised the impact [a two-metre social distancing] rule has in an 82,000-seater stadium but one metre has a very different impact," he said.
"We've run every model so we've got a sense of what that does."