UEFA announced in August a series of changes to its premier club competition from 2018, including guaranteeing a place for the top four clubs in the four top-ranked associations to leave only 16 spots for the rest of the continent.
European football's ruling body also plans to give precedence to former winners of the competition regardless of their current form.
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However, Lars-Christer Olsson, chairman of European Professional Football Leagues (EPFL), said on Wednesday that there was almost unanimous opposition to the changes across Europe, including from England and Spain.
That is due to a fear that they are the first steps towards a closed Champions League for the chosen few of Europe's elite clubs.
"The deal is not done," Olsson told delegates at the Leaders in Sport Business Summit at Chelsea's Stamford Bridge ground.
"The new UEFA president (Slovenian Aleksander Ceferin) has said he will look at it again and I am confident that we can change it," he added.
Olsson dismissed suggestions that his organisation lacked the power to influence UEFA or compete with that of the biggest clubs and he is expecting progress after a meeting on Oct. 21.
"The procedure has been slow as well as wrong and we were not consulted," he said.
"We have to come to a conclusion soon and that means changing some of the decisions already made. With a new UEFA president I think there is an opportunity to bring it back to the table.
"We agree there needs to be a certain adjustment to Champions league and Europa League and of course the big clubs should be heard and are important, but you have to keep a door open for those who want to get into the system - the dream has to remain available."
Olsson said his organisation was considering various options should UEFA not listen to its protest, adding that domestic leagues could in future schedule matches on Champions League nights.
Scotland is one of the lower-tier nations likely to suffer should the proposals go ahead and Neil Doncaster, CEO of the SPFL, said they were "hugely damaging".
"I've never seen the game in Europe so united against a set of proposals," he told reporters.
"A closed shop is clearly what a number of clubs would like to see and it's outrageous that UEFA has presided above that.
"It's totally crazy and the first step towards a private league."
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