Ceferin, who has been Uefa president since 2016, has overseen an agreement on a new-look 36-team Champions League but made clear his disdain for the ESL project.
"We are all united against this nonsense of a project," he said.
"I cannot stress more strongly how everyone is united against these disgraceful, self-serving proposals, fuelled by greed above all else.
"[It is a] cynical plan, completely against what football should be. We cannot and will not allow that to change.
"Players who will play in the teams that might play in the closed league will be banned from the World Cup and Euros. We urge everyone to stand tall with us as we do everything in our power to ensure this never ends up in fruition.
"This idea is a spit in the face of all football lovers. We will not allow them to take it away from us."
Anyone else feels it is super ridiculous that UEFA is talking player bans and not club bans. All the threats maybe futile in the end, but if he wants to threaten someone with dire consequences, then it should be the clubs.