The failed Super League hold-outs are facing a two-year ban from the Champions League.
Disciplinary proceedings have been opened against Real Madrid, Barcelona and Juventus over their involvement in the aborted European Super League, UEFA has announced.
The three teams were the only ones of 12 original breakaway clubs who did not subsequently renounce the competition and reaffirm their commitment to UEFA.
A UEFA statement read: "Following an investigation conducted by UEFA ethics and disciplinary inspectors in connection with the so-called 'Super League' project, disciplinary proceedings have been opened against Real Madrid CF, FC Barcelona and Juventus FC for a potential violation of UEFA's legal framework."
UEFA's move raises the prospect of the three clubs being sanctioned, with some reports suggesting they face expulsion from UEFA competitions such as the Champions League for a period of two years.