The Red Devils, who have an estimated 333 million fans around the world, topped the list with a worth of $1.86 billion, just ahead of the Dallas Cowboys ($1.81 billion).
The top 50 included seven soccer teams, with Real Madrid coming in fifth and Arsenal seventh. Barcelona, considered the world's best team, came in at a relatively low 26th despite their on-field success.
All 32 franchsises in the National Football League (NFL) made the top-50 with six, Dallas, Washington, New England, New York Giants, Houston Texans and New York Jets in the top 10.
The only team in the top 10 that did not play football was Major League Baseball's New York Yankees, who were third overall.
Ferrari was the top motor racing team, listed at 13th, while the New York Knicks (47th) were the leading basketball franchise.
The Forbes Top Ten teams:
1. Manchester United
2. Dallas Cowboys
3. New York Yankees
4. Washington Redskins
5. Real Madrid
6. New England Patriots
7. Arsenal
8. New York Giants
9. Houstan Texans
10. New York Jets
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