New England Patriots quarterback Tom Brady opened a six-day tour through China and Japan over the weekend as a representative of Under Armour. To promote his branded recovery sleepwear, Brady will hold clinics in Beijing, Shanghai and Tokyo.

Make no mistake. This is the kind of international campaign reserved for the most recognizable sports stars in the world. But it's notable, frankly, because this particular star is an NFL player. As the ESPN World Fame 100 rankings demonstrate, the NFL in a global sense holds nothing close to the dominance that it enjoys in the United States.

Brady checked in at No. 21 on this year's list of the most famous active athletes in the world, compiled with a formula that uses data on endorsements, social media following and Google trends scores. He was one of only two NFL players in the top 50 -- Carolina Panthers quarterback Cam Newton ranked No. 47 -- in what was an accurate depiction of the NFL's challenge in pursuing its goal of developing 400 million international fans.

For context, consider that the top 50 included 19 soccer players and nine from the NBA. Two cricket players ranked ahead of Brady. David Schwab, an executive vice president at Octagon who develops global marketing strategies for celebrities and brands, said the rankings reflect the NFL's current place in the worldwide sports marketplace.

"The drawback of the NFL is the domestic nature of the games played," Schwab said, "along with the television coverage and the participation at a youth level. It's not a sport that people are playing internationally, or really even seeing a lot of relatively. If you take a sport like basketball, you have more international players in the NBA, you have the Olympics component and heavy participation around the world."

Indeed, the NBA has a two-decade head start in Asia. Its superiority is especially notable in China, a country of 1.4 billion people that heavily influenced the ESPN 100 list. Not a single Major League Baseball player made the cut, for instance, reflecting its minimal impact in China despite heavy interest in Japan and Korea.

Kobe Bryant's first promotional trip to China came in 1998, nearly 20 years before Brady's. Yao Ming's 2002 arrival with the Houston Rockets further spurred Chinese interest, as did regular corporate visits from stars such as Bryant, Allen Iverson, LeBron James and Kevin Durant. The NFL has struggled to gain a foothold in a country that, in U.S. sports terms, is the equivalent of 1.4 billion potential new fans. There is a smattering of independent efforts to build a participation base, but it remains at the lowest of grass-roots levels.

I spoke last year to Zach Brown, a former Arizona State player who helped start a club-level Chinese league earlier this decade. How did he recruit players? By handing out business cards on Shanghai streets that read, in Chinese: "I play American football. You look like a dude who could play. Contact us here."

Efforts to accelerate NFL interest there have been met with internal resistance. Mark Waller, the NFL's executive vice president for international, has hopes of staging at least a "one-off" regular-season game that would deposit NFL-branded football in front of Chinese eyes, but logistics have proved difficult.

NFL executive vice president for international Mark Waller has said that in the next 10 years, "I think we will have at least one or two franchises outside of the U.S." Kirby Lee/USA TODAY Sports

In the meantime, the NFL is laboring to find its own Yao. Its U.K.-based international office engineered the process that got German receiver Moritz Bohringer drafted by the Minnesota Vikings. Bohringer spent 2016 on the Vikings' practice squad, and last week the league placed four European players on NFC South practice squads for the season. "That provides individual human-interest points for a particular fan base," Schwab said. "But if you can't regularly watch what they're doing on TV, and on a day-to-day basis you don't live or know the sport, it's hard to maintain the relevance."

So how has Brady found room in this unlikely space?

It's not simply the fact that he has been the 12-time Pro Bowl quarterback on a team that has played in seven Super Bowls, winning five, during the past 15 years. He also has pursued, in an overt way, an international sponsorship model. While other quarterbacks largely have paralleled the NFL's own list and style of corporate sponsors (think: Peyton Manning's work with Papa John's and Nationwide Insurance), Brady is following what you might call the David Beckham model. He has teamed up with "lifestyle" brands such as UGG, Tag Heuer, Stetson and Aston Martin. And Brady's wife, supermodel Gisele Bundchen, provides the same kind of global relevance as Victoria Beckham.

Brady, however, is the clear exception for a league of mostly hidden faces from an international perspective.

On the surface, the ESPN World Fame 100 list might seem to reflect a massive opportunity for NFL growth. But a closer inspection illustrates what appear to be significant obstacles. Football is king in America, but fans around the world are more likely to identify with top stars in soccer, the NBA, cricket, track and field, golf, tennis and even MMA.