Real Madrid, Barcelona and Juventus are the only three clubs from the original Super League project yet to withdraw; UEFA has opened a disciplinary investigation against the three rebels.
The nine clubs who withdrew out of the Super League, including AC Milan, signed the Club Commitment Declaration with UEFA on Friday.
The Super League project was abandoned within 72 hours of its announcement last month amid considerable fan protests and pressure from governmental bodies and players as well as some coaches.
UEFA's statement reads the following:
"In accordance with Article 31(4) of the UEFA Disciplinary Regulations, UEFA Ethics and Disciplinary Inspectors have today been appointed to conduct a disciplinary investigation regarding a potential violation of UEFA’s legal framework by Real Madrid CF, FC Barcelona and Juventus FC in connection with the so-called ‘Super League’ project."
"Further information regarding this matter will be made available in due course."