Manchester United has signed a three-year sponsorship deal with sports betting company Bwin for an undisclosed amount, making it the club's "official online gaming and betting partner".
Bwin is the shirt sponsor of Real Madrid and a partner to Bayern Munich.
Last week, United floated its shares on the US stock market, raising $233m (£150m), less than originally hoped.
The flotation values the club at more than $2.3bn, making it one of the biggest sports clubs in the world.
Last month, the club signed a shirt sponsorship deal with US car brand Chevrolet which will begin in the 2014-15 season.
Manchester United now has 28 different sponsors, with Aon the club's main shirt sponsor.
"As Europe's leading online sports betting operator, football is fundamental to our long-term success, making up approximately half of our total sports betting revenue of 261m euros ($320m; £204m) in 2011," said Norbert Teufelberger, co-chief executive of Bwin's parent company, Bwin.party.
"Man Utd has 569 million followers outside of Europe, providing us with a great opportunity to offer jointly designed and innovative products in countries that do not yet allow real money online sports betting," he said.
Manchester United has been controlled since 2005 by the Glazer family, the billionaire US sports investors who also own the Tampa Bay Buccaneers American football franchise.
About half of the $233m that the club raised from its flotation will go to paying off the club's debts, with the rest going to the Glazers.
Shares in the club closed down at $13.77 in New York, closing below their flotation price of $14 for the first time.