Clubs signed up to the new European Super League (ESL), including Manchester United and Manchester City, are fielding calls from players and agents worried about the implications of the bombshell plans, sources have told ESPN.

A number of top players under contract at the six Premier League clubs signed up to the new venture -- United, City, Liverpool, Chelsea, Tottenham and Arsenal -- have raised concerns about UEFA's threat to ban them from playing for their countries at international tournaments.

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There has been a suggestion that suspension could come into force as early as the European Championship this summer.

Sources have told ESPN that representatives who have managed to contact United in the 48 hours since the Super League announcement on Sunday night, have been told the club are confident players cannot be banned from international competition.

Super League chairman Florentino Perez said he was "completely sure" that league participants won't be thrown out of this season's Champions League over their role in the proposed breakaway group.

However, a host of players remain upset that their participation at future World Cups has been gambled against the huge financial rewards offered by the ESL without consultation, either face-to-face or through unions.

Sources have told ESPN that United do not view the move as a breakaway from the Premier League and remain convinced the threat of expulsion is empty because of the huge commercial appeal of the big six, particularly with regards to the negotiation of broadcast deals.

United, led by the Glazer family and executive vice-chairman Ed Woodward, want to begin talks with UEFA immediately about how the ESL can fit into the football schedule.

Sources have told ESPN the club plan to present evidence that early rounds of existing European football are "stale and predictable," backed up with stadium attendances and TV viewing figures.

There is a belief that the only way forward is to allow the biggest teams to play each other more regularly rather than just during the final weeks of the season.

The rebel clubs -- six from the Premier League, Real Madrid, Barcelona, Atletico Madrid, AC Milan, Inter Milan and Juventus -- insist the ESL will provide greater financial support for the football pyramid with a planned €10 billion in solidarity payments to be distributed over an initial 23-year period.

If the plan goes ahead, there will be 15 permanent places, with clubs outside the ESL given the opportunity to compete for five qualifying places through UEFA competition or national leagues.