England coach Eddie Jones believes increasing the number of teams in the Six Nations would be a mistake.
Reports have suggested South Africa could join the competition in 2023, but there has also been speculation that an eight-team event might be introduced.
“It’s called the greatest rugby tournament in the world and I think it is,” Jones insisted.
“So why would you want to add other teams that are going to decrease the level of competition?”
There has also been a suggestion that Fiji would also like to join and could play their ‘home’ games in France.
The last change to the structure of the event was in 2000 when Italy became the sixth nation.
Since then they and Scotland are the only teams not to have won the title.
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“You want the best teams playing against each other,” Jones added. “There’s something about the Six Nations – because of the history of the relationships between the nations, it makes it more outstanding.
“Someone was giving me a history lesson on Scotland and the number of different things that have happened in the rivalry with England. 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.”
Jones drew parallels with Super Rugby, the southern hemisphere competition for club teams which began with 12 sides but increased to 17 before settling on its current 15.
“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.”