MLS commissioner Don Garber said: "David was really a home run for us, to use a baseball analogy.
"He's going to make the £125m when his five years are up - I really believe that. Just look at what he's been able to generate this year. He is just an incredible marketing machine.
"And a lot of that has to do with him being quite the celebrity. If I was a sponsor, I would want him to represent me because he's just a quality guy.
"I hope to see at some point, certainly during my tenure as commissioner, players like that in Major League Soccer. And with Beckham being successful and being signed, it's hard to imagine you wouldn't see players like that in MLS."