A breakaway Women's European Super League would be "devastating" for the sport, says Uefa head of women's football Nadine Kessler.
Sunday's announcement of a new midweek competition featuring 12 confirmed clubs also included a women's version.
"The news comes without any consultation," Kessler wrote in an open letter on Twitter.
"It comes at a time when the Uefa Women's Champions League is about to see a transformative change."
She added: "In other words it is a direct threat to all the plans we have carefully crafted, together with the European Club Association (ECA), your clubs and the leagues for the new Women's Champions League."
Next season's Women's Champions League will feature a 16-team group stage as well as centralised marketing and TV coverage.
Few details have emerged from the ESL's founders as to how a women's version would look.
In its initial statement it said: "As soon as practicable after the start of the men's competition, a corresponding women's league will also be launched, helping to advance and develop the women's game."
Manchester City manager Gareth Taylor, who led his side to the Champions League quarter-finals this season, added: "We will see what happens in the future. I trust the club - we trust the club - to make the right decisions. We're not part of making those decisions.
"My take was that it was more solely focused on the men's game, then the part around it potentially happening in the women's game as well was kind of thrown in late and almost at the bottom of many other bullet points."
Of the 12 clubs who have agreed to take part in the new men's competition, Chelsea and Barcelona are represented in the last four of this season's Women's Champions League.
Lyon, the leading team in women's European club football with five Women's Champions League titles, were knocked out by Paris St-Germain in the quarter-finals of this season's competition, while Bayern Munich make up the final four.
Last month the ECA announced its first women's football strategy, including plans to introduce a second-tier European club competition.
"Clubs need to be able to have the ambition of being part of the top of European women's club football, the Uefa Women's Champions League," Kessler said.
"With a closed European Women's Super League, this is not possible.
"Such a development would be equally devastating for national leagues who have made enormous efforts to professionalise the women's game.
"And we do not only need more clubs, but a better balance between those clubs, so that more than just a few standout players can thrive on it.
"The value of our sport matters in times when greed seems to overshadow the broader needs of society and football as a whole. Solidarity matters."
Analysis - 'a travesty without European giants Lyon'
BBC Sport's Emma Sanders
There is a general feeling that women's football was an afterthought in the plans for a European Super League.
A solitary line in the statement lacked any detail on the implications it could have for women's football, and senior figures at a number of clubs are believed to have not been consulted on the plans.
In the assumption that the women's league equivalent would include the same 12 founding clubs, it would be a travesty without European giants Lyon - who picked up a fifth Champions League title in a row last year - and Wolfsburg, who have appeared in five of the last eight finals, winning two.
Liverpool, whose women's side currently compete in the domestic second tier, and Tottenham, who were only promoted to the Women's Super League in 2019, would look very out of place among Europe's supposed elite.
There would also likely be animosity towards Real Madrid, a women's team only formed last year; Manchester United, who were created in 2018; and the inclusion of two Italian sides despite the nation having never previously had any representation in a Women's Champions League final.
Aside from the obvious exclusion of those big European teams in the league, there is concern for the wider impact on grassroots football and domestic leagues which are not yet sustainable.
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