That's according to Jason Bernstein, senior director of programming and acquisitions at ESPN, who spoke with Tennis.com's Steve Tignor after the U.S. Open.
This may be news to Novak Djokovic and Andy Murray fans. Maria Sharapova loyalists are probably shocked.
I'm a die-hard tennis fan. I wake up at ridiculous hours in the morning to watch Australian Open matches live. But I'm in the minority in this country.
I know that unless the players are American or have reached Greatest of All Time status, most Americans couldn't care less.
Face it, more Americans are fixated on fantasy football than on real tennis players. Casual tennis fans don't care about players whose names they can't pronounce who come from places they've never been.
Not even an Americanized Russian like Sharapova piques our interest. Sharapova receives twice as much money in endorsements as Serena Williams. However, the Russian fails to move the ratings needle in this country.
When it comes to women's tennis, the ratings begin and end with Serena. This year's U.S. Open final between Serena and Victoria Azarenka scored a 4.9 rating, according to Sports Business Daily (subscription required). The men's final, played on Monday, garnered just a 2.8 in the overnight ratings.
Bernstein told Tignor the "Serena factor" played a major part in those ratings. "She's a proven ratings star, especially in the United States."
He said that while Federer and Nadal draw well, Djokovic and Murray haven't caught on with Americans.
Bernstein believes it takes time for Americans to warm up to non-Americans. Federer and Nadal have been winning for a while. They've grown on us. And even though Federer is slipping, casual fans just aren't ready to embrace Djokovic and Murray.
Until there is another American male to challenge the "Big Four," ratings for men's matches will continue to trail any women's match that features Serena.
Serena Williams is fun to watch. Even when she's losing, she's animated and interesting. Her game has variety. The rest of the women's field is mostly baseline rallies and double-digit double faults.
Why are tennis ratings low?
That's another reason why Sharapova is not a big ratings winner. Her game is boring. The 2012 French Open television ratings (h/t 10sballs.com) for Serena's first-round loss (1.02) drew almost as many viewers as Sharapova's appearance in the championship final (1.7) on NBC.
As reported by Sports Business Daily (subscription required), this year's women's final received the highest ratings since 2002, when Serena played Venus; that match drew a 7.2 rating,
Federer, Serena and Venus are in their 30s, and network executives are trying hard to cultivate interest in other tennis stars. Coverage of the U.S. Open semifinals included interviews and features on Stan Wawrinka and Li Na.
But unless Wawrinka is playing Federer or Li is playing Serena, Americans won't be tuning in.