Real Madrid, Barcelona and Juventus are keeping their plans alive of going ahead to form a breakaway European Super League.
The nine other rebel clubs reached settlements last week to commit to UEFA competitions and pay millions of euros (dollars) in forfeits of future prize money and donations to a UEFA-run charity.
While AC Milan and Inter Milan backed out of the ill-fated bid to form a breakaway competition, Juventus remains the lone holdout in Italy.
The three clubs are the only ones from the original 12 yet to renounce the proposed competition that would guarantee its founding members involvement every season, instead of having to qualify.
As fans protested on the field against United's owners - the Glazer family - flares were set off and thousands more supporters filled the concourse outside Old Trafford.
The American investment bank said on Monday it had committed 3.25 billion euros as start-up capital for the league which hreatened to devalue Europe's top domestic leagues.
The Super League, which provoked a backlash by other clubs, fans and authorities around Europe, was announced by a dozen top clubs in England, Spain and Italy on Sunday.
Many feel these clubs could face sanctions from UEFA or their respective associations but La Liga president Javier Tebas said that they are in no hurry to take action against these clubs.
Withdrawal from European Super League was the right thing to do: Manchester City captain Fernandinho
Manchester City captain Fernandinho believes football has emerged victorious following the collapse of the breakaway European Super League.
Ronald Koeman does not believe Barcelona's involvement in the collapsed European Super League will have an impact on the club's performance in La Liga.
After the aborted attempt to form a European Super League, Liverpool owner John Henry attempted to regain the trust of fans with an apology video.
The competition's announcement on Sunday, made by 12 founding clubs including Manchester City, Chelsea, Arsenal, Liverpool, Manchester United and Tottenham Hotspur, was met with widespread criticism.
The Super League plans have been widely condemned by the football authorities in England, plus UEFA and FIFA, as well as by the British government, and appear to be deeply unpopular with fans.
Rio Ferdinand has slammed the club for being involved in the formation of a breakaway European Super League.
Real Madrid President Florentino Perez has brushed aside threats from UEFA President Alexander Ceferin.