Ireland won the Six Nations title with a match to spare in 2018
The Six Nations is considering an offer from private equity firm CVC to sell a stake in rugby's oldest championship.
It is believed it could provide a windfall of more than £100m to each union but would mean partly surrendering control of the competition.
It comes as the power-brokers of the world game meet in Dublin this week over the proposed Nations Championship.
World Rugby will present its vision for the future of the sport on Thursday.
However, if the Six Nations decide to sell to private equity, it would almost certainly kill the chances of the revolutionary Nations Championship getting off the ground.
The Six Nations unions - England, Ireland, Scotland, Wales, Italy and France - have been in talks for the past 18 months over pooling their commercial interests, a strategy dubbed 'Project Light'.
The interest from CVC - one of a handful of possible options - means the Six Nations face a dilemma between selling to private money, or embracing the World Rugby-sanctioned Nations Championship.
It is understood CVC's offer is for an approximate 30% share in the Six Nations. Sources at the unions have not denied an offer is on the table but insist a deal is not imminent.
Aside from the interest from private equity, a number of Six Nations unions have already voiced their concerns over the introduction of promotion and relegation, which would be part of the Nations Championship.
CVC bought a minority shareholding of 27% in England's Premiership Rugby in December.
What are the latest World Rugby proposals?
World Rugby's Nations Championship would feature 12 teams in each of its three divisions.
The top division would be made up of a northern conference - which would be the six Six Nations sides - and a southern conference, which would feature the four Rugby Championship sides (New Zealand, Argentina, Australia and South Africa) and two others, expected to be Fiji and Japan.
Each team would play each other once a year, either through their own competition, or in one of the summer or autumn Test windows.
The Nations Championship would provide top-level exposure to the likes of Fiji, protecting and enhancing the game in the Pacific Islands as a result.
It would also include promotion and relegation to provide a pathway for emerging nations.
As reported by the BBC on Monday, the semi-final stage of the competition will be taken away to help with player welfare, meaning the top team in each conference would face off in a showpiece final.
This would mean the maximum number of matches a nation would play each year is 12, with the majority playing 11. However, it is believed New Zealand and Australia will be permitted to stage an extra Bledisloe Cup match, as is tradition.
The Nations Championship would ensure every game is competitive, which would drive up television figures and commercial interest, and would ensure nations play the same, or fewer, matches than they do currently.
The final would take place at the end of the year, ideally at a neutral ground in the northern hemisphere, with a £2m pot being shared between the winners and the runners-up.
Iconic sporting stadia such as Barcelona's Nou Camp have been mooted as possible final venues.
Promotion and relegation play-offs would take place on the same weekend as the final, although it is understood there would one four-year cycle before promotion and relegation is introduced.
Six Nations - money or global vision?
The future of the Nations Championship concept - and along with it the future of the international game - hangs on what route the Six Nations decides to take.
Selling to private equity would ensure a windfall for the six countries, but would likely end the chances of a unified global competition being formed.
The Scottish and Irish unions are thought to be especially opposed to the Nations Championship, and are keen on the opportunities provided by the likes of former Formula 1 owners CVC.
The Rugby Football Union is also thought to be lukewarm on the Nations Championship, but has promised to travel to Dublin with an open mind.
While the Nations Championship is expected to provide a 40% uplift in revenues, without surrendering control, the Six Nations may be swayed by the sheer size of CVC's offer.
However, CVC's motives are expected to be entirely financial, which could result in the Six Nations being taken off free-to-air television, while a 30% stake would mean 30% less revenue for each country year-on-year.
According to the Welsh Rugby Union chairman Gareth Davies, rugby union is at its "most challenging and dynamic time since the game went professional in 1995", with the next few months pivotal in shaping the long-term future of the sport.
