Ceferin said he is "sick and tired" of addressing the idea of a "nonsense" breakaway league and accused the rebel clubs of plotting against UEFA at a time of crisis in Europe amid the ongoing Russian invasion of Ukraine.
"I'm sick and tired of speaking of this non-football project," Ceferin told the Financial Times Business of Football Summit in London via video link Thursday.
"Look, first they launched their nonsense of an idea in the middle of a pandemic; now we're reading articles every day that they are planning to launch another idea now in the middle of a war.
"Do I have to speak more about those people? They obviously live in a parallel world.
"And while we are saving players together with other stakeholders, while we are working to help in a terrible situation, they work on a project like that."
Juventus chairman Andrea Agnelli, who was the former head of the European Clubs Association and one of the ringleaders of the short-lived breakaway plans, was seated in the front row at the event while the UEFA president lambasted his actions. The Daily Telegraph reported that Agnelli has not given up hope of a breakaway league.
Speaking at the Financial Times Business of Football Summit later on Thursday, Agnelli wouldn't be drawn on any specific plans to restart the project but insisted that the idea was not a failure and repeated his claim that European football was in need of reform.
This week, Ceferin and UEFA worked with the Ukraine Football Federation to aid the evacuation of Brazilian footballers from Kyiv.
"We're all just hoping and praying that the war stops. This madness should stop as soon as possible," Ceferin added.
Meanwhile, UEFA plans to introduce a "Swiss model" for the 2024-25 Champions League tournament that will see each club play 10 group games, rather than six, before advancing to a 16-team knock-out system in the second half of the season.
The plan also includes two Champions League qualification spots for teams that have long histories playing in the competition.
Ceferin rejected accusations that UEFA's plans were akin to the European Super League plot, saying: "I think, today, there's a meeting of the working group between the ECA and UEFA and it will be more places for smaller and mainly, to be honest, mid-size leagues."