I wish I were Michael Phelps. I bet you do, too. He's fast. He's covered in gold. And he's about to become filthy, filthy rich.

Most people don't expect to see a swimmer show up on MTV Cribs, but the endorsement deals that Phelps is rumored to be staring at are just silly. Some have thrown around $40 million to $50 million a year. A few have mentioned $100 million as a nice round number for what he could earn from sponsors.

Some endorsements could make a lot of sense -- Nike (NYSE:NKE), Speedo (a division of Warnaco (NYSE:WRC)), Coca-Cola (NYSE:KO), McDonald's (NYSE:MCD) -- those are all names where slapping a famous face on a product can instantly lead to explosive sales. Speedo, for example, expects to sell $5.5 million of those swim pants that Phelps wears (although I'm guessing most people will just give them a test run in the bathtub, then hang them up for good).

One big Phelps sponsor I can't seem to understand is Visa (NYSE:V). We don't know just how much the credit-card king plans on paying him, but I'd assume it's not chump change. But is a Phelps endorsement worth the money? I can't see how it would be. I just can't see how promoting a face -- even someone as colossal as Phelps -- will end up being financially worthwhile for a credit-card company.

Visa and rival MasterCard (NYSE:MA) undoubtedly compete for market share, but how much do people really care what moniker sits at the bottom of their card? Not many, I'd assume. When signing up for credit cards, most people care about things like interest rates and rewards, not whose processing system the card uses. Visa touts its cards as the only ones accepted at the Olympics, but most people know that if a merchant accepts Visa, it generally also accepts MasterCard. The two companies are virtually ubiquitous.

Even if people do swarm to Visa in a Phelps frenzy, how much money would be brought in? Well, Visa currently has around 1.6 billion cards in circulation. It's expected to earn around $1.7 billion this year, or around $1 per card. Again, it's uncertain how much Visa intends on paying Phelps, but you can see that it would take an awfully large surge in customers to cover however many millions he gets.

No question about it, Visa has brand recognition. It's probably one of the most recognizable logos in the world. But at some point, leveraging a brand name in a market where customers probably aren't brand-sensitive seems fruitless.

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Fool contributor Morgan Housel doesn't own shares in any of the companies mentioned in this article, but has the doggy paddle down pat. Coca-Cola is a Motley Fool Inside Value recommendation. The Fool has a disclosure policy.