United retained the title thanks to lucrative global sponsorship deals with AIG, Turkish Airlines and DHL.
Spanish giants Real Madrid are second at $1.88bn while the New York Yankees and Dallas Cowboys are tied at third with $1.85 billion.
The Los Angeles Dodgers and New England Patriots are tied for sixth at $1.40 billion, followed by Barcelona at $1.31 billion, the New York Giants at $1.30 billion, and Arsenal at 1.29 billion. The Dodgers recently were sold for $2 billion, the most for any professional sports team.
NFL's 32 teams are on the list of 50 most valuable franchises while seven Major League Baseball teams earned their spots.
NBA's Los Angeles Lakers are valued at $900 million, 35th overall, the highest in the sport while New York Knicks come No. 43 with $780 million.
Manchester United, earlier this month, had applied to list on the US stock market in share sale aimed at raising $100m. The most-supported club in the world said the funds raised would be used to repay debt.
The club has been managed by the Glazer family since 2005. The billionaire US sports investors who also own the Tampa Bay Buccaneers American football franchise.