The governing body of European football said that "in a spirit of reconciliation" the nine clubs had agreed to a "Club Commitment Declaration" and accepted a five percent cut in their European revenue for one season.
However, three clubs, Barcelona, Real Madrid and Juventus, did not sign the declaration.
UEFA said it "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 statement concluded.
The nine clubs that opted out of the project -- Tottenham, Arsenal, Manchester City, Manchester United, Chelsea, Liverpool, Atletico Madrid, Inter Milan and AC Milan -- have agreed to a series of "reintegration measures".