United's estimated operating income was $111 million, $1 million behind Real Madrid, which was valued at $1.285 billion, according to Forbes, which values the top clubs annually.

By comparison, the most valuable US professional sports team is the National Football League's Dallas Cowboys, which Forbes valued at $1.5 billion last September.

Not surprisingly, the magazine estimated British soccer star David Beckham, who plays for US-based Major League Soccer's Los Angeles Galaxy, was ranked as the highest earning player at $49 million. He previously played for both United and Real Madrid.

United, known as the Red Devils, are the reigning English Premier League champions, and reached the European Champions League final on Tuesday. The club is owned by US businessman Malcolm Glazer, who bought the team in 2005 and also owns the US football Tampa Bay Buccaneers.

Four of the clubs in the top 10 are from the English Premier League, considered the richest soccer league in the world. The top 10 also includes two clubs each from Spain, Germany and Italy.

Forbes values teams based on what they have sold for in the past relative to sales and profits, broadcast agreements and debt from new and pending stadium deals.

Rounding out the top-five list of valued soccer clubs were Arsenal (with a value of $1.2 billion), followed by Liverpool ($1.05 billion) and Bayern Munich ($917 million), according to Forbes.

The second five were AC Milan ($798 million), Barcelona ($784 million), Chelsea ($764 million), Italy's Juventus ($510 million) and Germany's Schalke 04 ($470 million), according to Forbes.

Forbes also reported that Arsenal's Emirates Stadium, completed in 2006 at a cost of $860 million with a capacity of 60,432, is a gold mine, generating $6 million a game.