A disciplinary investigation has been opened against Real Madrid, Barcelona and Juventus in connection to their involvement with the European Super League project, UEFA has announced.

The three clubs were key drivers in the breakaway league's official foundation on 18 April and did not join the other nine Super League clubs in renouncing the breakaway competition and renewing their commitments to UEFA last Friday.

UEFA released a statement on Wednesday, which read: "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, Barcelona and Juventus in connection with the so-called 'Super League' project.

"Further information regarding this matter will be made available in due course."

The prospect of disciplinary action appeared inevitable last Friday when a statement confirming the peace accord with nine of the clubs ended: "UEFA has reserved all rights to take whatever action it deems appropriate against those clubs that have so far refused to renounce the so-called 'Super League'.

"The matter will promptly be referred to the competent UEFA disciplinary bodies."

The nine other clubs - including the Premier League's 'Big Six' committed themselves to existing national and UEFA competitions, with the threat of heavy fines and expulsion if there was any renewed attempt by any one of them to break away.

However, Real, Barca and Juve issued a joint statement on Saturday standing by the Super League project, stating it was lawful and that it would be "highly irresponsible" of them not to continue to look at ways to answer what they see as the "existential questions which threaten football".

Manchester United confirmed that a goodwill payment agreed as part of their reintegration would be met personally by the Glazer family.

UEFA also said it would withhold five per cent of next season's competition revenues from each of the nine clubs, and again United said this lost money would be covered by the Glazers.