An antitrust lawsuit would not prosper. Consumers would still have alternative choices to enjoy football, and clubs could still participate in other competitions/federations.
There are plenty of precedents that would not allow to block the ESL, even where one company would have an absurd amount of market share (dominant position). As long as the above mentioned rights are not restricted, it would not be considered an anti competitive practice.
Sauce: I wrote a thesis on antitrust and merger control.