England coach Eddie Jones has said experience of southern hemisphere rugby makes him wary of expanding the Six Nations Championship to include South Africa.
Tournament organisers have played down reports the world champions could join an expanded Six Nations in 2024.
"It (the Six Nations) is called the greatest rugby tournament in the world and I think it is," said Jones.
"So why would you want to add other teams that are going to decrease the level of competition.
"I can only talk from experience. Super Rugby was the golden egg of rugby -- brilliant, 12 teams, competitive. As soon as it had gone to 14 and 15, it had lost its allure.
"You want the best teams playing against each other. There's something about the Six Nations -- because of the history of the relationships between the nations, it makes it more outstanding."
England, beaten by South Africa in last year's World Cup final, revived their Six Nations title hopes with a 13-6 win over Scotland at a storm-tossed Murrayfield on Saturday.
- 'Harder contested than the World Cup' -
"Someone was giving me a history lesson on Scotland and the number of different things that have happened in the rivalry with England," added Jones.
"So there's a lot of meaning to a lot of people for a game like this.
"The competition is much harder contested than the World Cup. It's become a lot more physical and it's only going to get more so.
"You don't want this type of game every week, but southern hemisphere coaches certainly admire the Six Nations.
"From the first Six Nations I did to now, I think we've seen a general rise in the quality of the teams.
"Ireland, Wales, Scotland, England -- they are all operating at a high level now. The gap between the teams is so small."
Storm Ciara effectively ruined Saturday's match in Edinburgh as a contest, with no roof at Murrayfield to protect the ground from the elements as is the case at Cardiff's Principality Stadium.
But Jones, who saw replacement prop Ellis Genge driven over for the decisive try in the 70th minute, was delighted by the way England responded to their tournament-opening 24-17 defeat by France in Paris.
"I loved it. Rugby is a winter sport. Until we make it a summer sport we should be playing in winter conditions," he said.
"The players have got to adapt to the conditions and find a way to win.
"To come up here and do that after we got a bit of a kick in the guts against France is one of the most satisfying wins we've had."
Six Nations expansion warning - England coach Eddie Jones