World Rugby's deadline for the Nations Championship is likely to run into next week as talks continue over whether the new concept will get off the ground.
The governing body had set a deadline of Friday for formal expressions of interest from the unions.
However, it is understood this will not be enforced so more discussions can take place before any due diligence.
Sources say there has been "real engagement" as parties try to work through the various obstacles.
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Scheduled to launch in 2022, the Nations Championship would see a top division of 12 teams from both hemispheres play each other once in a calendar year, either through traditional competitions like the Six Nations or an enlarged Rugby Championship, or in summer or autumn Test windows.
The top two teams would then meet in an end-of-year showpiece final.
Backed by a £5bn offer from sports marketing giants Infront, the Nations Championship would include relegation and promotion between divisions after an initial moratorium.
However, the prospect of dropping out of the Six Nations has alarmed leading northern hemisphere unions, with interim RFU boss Nigel Melville stating relegation could be "catastrophic".
World Rugby insists the second division will be both lucrative and competitive, and has spent much of the past few weeks trying to convince the concerned Six Nations unions.
It is believed the southern hemisphere superpowers who make up Sanzaar - New Zealand, South Africa, Australia and Argentina - are fully in support of the Nations Championship as they battle financial difficulties and a player drain to Europe.
Of the leading northern unions, France have expressed their support for the world league, while the Welsh and English unions are thought to be amenable to the concept in theory.
The Irish and Scottish unions remain the most opposed, especially given the interest in the Six Nations from private equity giants CVC as well as other offers as part of 'Project Light', a scheme whereby the Six Nations unions pool their commercial rights.
Six Nations Limited - represented by chief executive Ben Morel - is also believed to be lukewarm about the World Rugby proposals.
However, while unanimity is needed in order for the Nations Championship to get the go-ahead, there remains optimism the concept is still alive.
"We are seeing more positivity from the staunch detractors," one source told the BBC, with another adding "this has a way to run".