Six Nations chief executive Ben Morel would be "cautious" about adding South Africa to the competition.
There has been renewed talk of incorporating the Springboks into the Northern Hemisphere competition, after the Bulls, Sharks, Lions and Stormers formed part of the United Rugby Championship.
SA Rugby chief executive Jurie Roux added fuel to the fire last month, saying, "We would need an invitation [to join] and we would definitely be interested.
“We are firmly aligned to the northern hemisphere now but we can only cross that [Six Nations] bridge when we come to it."
South Africa remain contracted to the Southern Hemisphere Rugby Championship until 2030, and Morel has put even more distance between the parties.
"It’s not currently a question," said the Six Nations chief executive, "My understanding is that South Africa are committed to the Rugby Championship and at the same time our focus is on July and November.
“The Six Nations has added to, and reduced, its number of teams in very few moments during its 140 years, so it is something that we would be very cautious of doing.”
Instead of adding South Africa to the Six Nations, Morel is instead content to more closely align his tournament with the Rugby Championship.
Talk of a Nations Championship/Global Nations League have been around since before the pandemic hit, with the original hopes it would launch in 2022.
But Morel has fleshed out the proposals ahead of this year's autumn window.
"It’s ‘24 onwards, I would say, that we are looking at right now," he told reporters, adding the July and November international windows would be kept sacrosanct.
Morel added, "Looking forward we are having a lot of discussions as to what could be the future of the international calendar when looking at July and November.
"That obviously needs to be compatible with player welfare and whatever adjustments we could make.
“We’re all pretty happy with what we have but that could be improved and whether that leads to a final or some sort of ranking that would be a positive to add.
"It is a complex matter but the Six Nations is playing a leading role in addressing that.”
Meanwhile, Morel also revealed that the Women's Six Nations will be kept in its own separate window. This year, the competition was played in April - weeks after the conclusion of the men's equivalent.
It led to increased visibility for the women's competition, as it was no longer squeezed into a busy international weekend.
“The specific window and showcasing of the women’s game and putting it in the limelight is something that we definitely want to continue," said Morel.
“The Six Nations next year will be in a separate window, but coming back to its original format with five matches per union. So, that will be happening right after the men’s.
"We will be announcing the precise fixtures shortly.”