The typical professional athlete's marketability is largely a function of his talent, and over a long enough time frame, his performance. Among NFL players, Peyton Manning, Tom Brady, Aaron Rodgers, and Drew Brees each make an average of $9 million a year in endorsements, according to Forbes. Each is unquestionably among the best in the game, each has at least one Super Bowl ring. 

Still, outliers exist. Michael Sam, the first openly gay player to be taken in the NFL draft, is one example. Sam's marketability stretches far beyond the football field, and after coming out in February, the defensive end has become a figurehead for the most important civil rights issue of our time. But does his endorsement potential rival Manning's, and the rest of football's elite?

The sponsorship pool is vast
As I wrote earlier this year, Sam's profile is attractive to a variety of sponsors. Nike (NKE 0.95%) is the most widely cited example, as the sports apparel company already has endorsement deals with the NBA's Jason Collins and the WNBA's Brittney Griner, both of whom are openly gay. Although an arrangement with Sam has yet to be announced, one could be around the corner ... assuming he makes the St. Louis Rams roster

Nike is also the official uniform provider of the NFL, and Sam currently has the league's second highest-selling rookie jersey behind Johnny Manziel, CNN reports.

Image via St. Louis Rams/ESPN.

Nike signed Manziel to a multi-year deal earlier this year that's likely in the eight-figure range

Sam's ability to keep pace with a player drafted more than 200 spots above him (Sam went to the Rams in the seventh round while the Cleveland Browns took Manziel at 22nd overall) and ahead of all other drafted players speaks volumes about his endorsement potential. If jersey sales are any indication, Sam is already more marketable than first-round picks like Jadeveon Clowney, Teddy Bridgewater, and Sammy Watkins.

Nike's not the only potential partner, though. Visa (V -0.48%) has already signed the defensive end, according to ESPN. The financial services giant released Sam's first TV spot last week. Titled "How you should judge Michael Sam," the commercial is part of Visa's #everywhere campaign.

General Motors' (NYSE: GM) Chevrolet, Macy's (NYSE: M), and Amazon (NASDAQ: AMZN) are just a few of the companies who've also aired LGBT-friendly ads in recent years -- it's reasonable to think they'd consider signing Sam. But, interestingly enough, that doesn't guarantee he'd reciprocate. 

In a recent interview with ESPN's Darren Rovell (via the Sports Agent Blog), Cameron Weiss, Sam's agent, revealed why:

We've been really selective with what we've done with Mike [Sam]. We don't want to give off the impression that he's "cashing in" on being gay. We want him to be seen as a football player. We want these ads to be focused on performance.

The Visa spot is a perfect example of this strategy. When others jump on board, they'll probably have to follow a similar blueprint. 

What's next?
Under the assumption Sam does accept more endorsements, the obvious question is: How much money could he make? Let's take a look at what other NFL stars are being paid.

Annual Endorsements of NFL Athletes*
Peyton Manning $12.0 million
Drew Brees $11.0 million
Tom Brady $7.0 million
Aaron Rodgers $6.0 million
Tony Romo $3.0 million
Ray Rice $1.6 million
Joe Flacco $0.9 million
Calvin Johnson $0.8 million
Clay Matthews $0.5 million
Matt Schaub $0.4 million

*In 2013, according to Forbes.

Offensive players have a clear advantage. Seven of the 10 most marketable NFL athletes are quarterbacks. Ray Rice and Calvin Johnson lead all running backs and wide receivers, respectively. Most noticeably, only one defender -- Clay Matthews -- makes the cut. The Green Bay Packers' linebacker has several endorsement deals, most notably with Procter & Gamble's (NYSE: PG) Gillette, Nike, and Fathead.

Given this precedent, then, it's tempting to think Sam's marketability will never rival someone like Manning or Brees. Also working against Sam is the fact that he'll likely be a backup for the Rams, who have one of the deepest defensive lines in football. Starters Chris Long and Robert Quinn have 85 career sacks between them.
 
In reality, though, none of the players on that list have even a sliver of the uniqueness Sam possesses. The American LGBT community represents an annual buying power of more than $700 billion, according to Witeck-Combs Communications. And as this market's sole representative in the country's most popular sport, the value of Sam's potential is theoretically infinite. 
 
Think of it in terms of basic economics: There's an obvious demand for LGBT athletes who play in the NFL, and he's the only supply available. Quite literally, Sam is a one-man monopoly. If a company wants to sign a star QB with a Super Bowl championship, for example, there are multiple options. If a hard-hitting, outgoing linebacker is needed, there's a handful to choose from. But someone who embodies the gay rights movement? No alternatives exist in football.
 
The bottom line
Despite this, I don't think Michael Sam will come close to the $12 million Manning collects from annual endorsements. It's likely that dozens, if not hundreds of companies -- small and large -- will want to build a relationship with the defensive end, sure. But remember what his agent said: "We don't want to give off the impression that he's "cashing in" on being gay." Translation: If the total value of Sam's deals flirt with eight figures, he'll call it quits.