Image source, Getty Images
England players Ellie Kildunne and Jess Breach play for Harlequins and Saracens respectively in Premiership Women's Rugby
R360's proposed four-team women's event is an exhibition-style showpiece that could leave players short of form and fitness, says Premiership Women's Rugby executive chair Genevieve Shore.
R360 - a big-money breakaway series that aims to launch in October 2026 - has reportedly approached high-profile players from the recent Women's World Cup about taking part.
England full-back Ellie Kildunne has said she is interested in learning more about it.
Shore said any recruits would miss out on the depth of England's nine-team PWR, which is widely considered the premier domestic club competition in women's rugby.
"I wouldn't describe what R360 are talking about as a league. Four franchises is not a league," she told BBC Sport.
"Four franchises is a short-term showpiece competition.
"It may generate brilliant revenue and fantastic audiences and be visible, or it may not, but it's definitely not a league.
"Playing maybe eight games, maybe 10 games - that is not getting you ready for international rugby.
"So where does that leave those players? I worry that they'll be in limbo."
On Tuesday eight of rugby's leading Test nations, including England, France and New Zealand, announced that any players - men or women - who sign up for R360 would be excluded from their national sides.
R360's first event seems likely to clash with the newly announced WXV Global Series.
Canada, runners-up at the World Cup, were not part of the joint statement.
Many of their players, including captain Alex Tessier and world player of the year Sophie de Goede, play in PWR.
About one in four players at the World Cup play in the league.
Shore said she would "totally understand" if any opted to move to R360 for a payday reportedly several times what is on offer in loss-making PWR.
"I would not blame any female at all for recognising her value or worth," she said.
"We want to see female athletes in any sport, whether it's rugby or football or tennis or cricket or whatever, get the value for the talents that they deserve.
"That's why we all swing our legs out of bed in the morning."
However, Shore said R360, which organisers say has attracted investment from a variety of funds and individuals, is fundamentally different to PWR, which supports the rest of the game.
"Our league houses just over 500 players, and they go from 18-year-olds up to players in their 30s with 100 caps for their country," Shore said.
"Our job is not just the athlete with 100 caps, though.
"Our clubs have invested millions in schools, in colleges, in university partnerships, in building out their pathway projects and work with the Rugby Football Union, who are doing the same.
"If R360 are a private, limited company they don't have to do that. Their purpose is to do something that's innovative and exciting at the top of the game.
"The one thing that you do read consistently is that they plan to break even in year two. So the goal is to make money for the people who invest in it."
The unions said in their joint statement that R360 was "designed to generate profits and return them to a very small elite, potentially hollowing out the investment that national unions and existing leagues make in community rugby, player development and participation pathways".
Yann Roubert, the head of the French club game, said, external on Wednesday that "you don't build a sport by bypassing those who build it".
R360 said it will put "players first" and offer the highest standards of support, and that the investment and attention it will attract can help the sport as a whole.