The Six Nations tournament - which features the national teams of France, Italy, England, Scotland, Wales and Ireland may be partly sold to a private equity firm.
It all comes as the Rugby World Cup starts in Japan this Friday.
The latest proposal could see CVC, the former owners of Formula One, take control of 15% of the commercial arm of the business.
Six Nations confirmed that negotiations are taking place and said in a statement they believe this investment would be vital for the long-term future of the sport.
They added they won't be making any further comments on it for now.
World Rugby's Chief Executive, Brett Gosper, responded to questions at a news conference in Japan. He said:
"I would have to say we don't know enough about the ins-and-outs of that deal, it is a bit shrouded so we cannot really comment at this stage whether it is good or bad.
"Certainly as big an investor in the sport as a private equity firm such as CVC would create influence and that could be in some areas something that could concern us.
"So it is important that we understand from CVC exactly what their medium to long terms plans are and from that we can react. It is a big early to evaluate where we are heading at this point in time," he added.
World Rugby's proposal to create its own vehicle to attract major investment in the sport via a World League involving both Six Nations and Rugby Championship teams New Zealand, Australia, South Africa and Argentina was rejected earlier this year.
The deal is not expected to be complete until after the Rugby World Cup, which finishes on the 2 November.