Two prominent NFL owners have a stake in a bookmaker as the first season with expanded legal sports betting in the U.S. gets ready to kick off.

New England Patriots owner Robert Kraft and Dallas Cowboys owner Jerry Jones have retained their investments in DraftKings, sources confirmed to ESPN, even as the company has shifted some of its focus from daily fantasy to traditional sports betting.

Kraft's and Jones' stakes in DraftKings are said to be small: less than 5 percent, according to sources. In a court disclosure, 21st Century Fox was the only company listed as owning 10 percent or more of DraftKings.

A Cowboys spokesman said Jones' investment in DraftKings is through sports hospitality company Legends, not the team. Jones and the Steinbrenners, owners of the New York Yankees, have been described as "principal owners" of Legends.

The Patriots declined comment.

NFL spokesman Brian McCarthy told ESPN in an email that current league policy "enables personnel to own equity interest in an entity that generates less than a third of its revenue from gambling-related operations."

DraftKings remains primarily a fantasy sports provider, however, CEO Jason Robins recently told Yahoo that he believes the company will be focused on sports betting in two to three years. Research firm Eilers & Krejcik Gaming pegged DraftKings' daily fantasy revenue in 2017 at $218 million.

If DraftKings' revenue from sports betting eventually eclipses the NFL's current standards and Kraft and Jones are forced to divest, it could be costly for the two owners and lead to another faceoff with NFL commissioner Roger Goodell.

For now, DraftKings' sportsbook is in its infancy and is offered only in New Jersey. The company is looking to operate in additional states that legalize sports betting.

On Aug. 1, DraftKings became the first company to launch a mobile sports betting app in New Jersey and has been taking bets the entire month, including on preseason games involving the Patriots and Cowboys and on future events like the odds to win the Super Bowl. The Patriots are the favorites at 6-1 to win the Super Bowl at DraftKings. The Cowboys are 28-1.

The NFL has been a staunch opponent of sports betting for decades and remains concerned about its impact on the integrity of the game. The NFL fought New Jersey's efforts to offer Las Vegas-style sports betting all the way to the U.S. Supreme Court.

In May, the Supreme Court ruled against the NFL and other major sports leagues and struck down the Professional and Amateur Sports Protection Act of 1992, the federal statute that restricted state-sponsored sports betting to primarily Nevada.

Since the ruling, Delaware, Mississippi and New Jersey have opened sportsbooks. The racetrack at the Meadowlands in New Jersey, which is adjacent to MetLife Stadium, home to the Giants and Jets, is offering sports betting.

The NFL is lobbying in Washington, D.C., for a federal framework to oversee sports betting. Sen. Orrin Hatch (R-Utah) has said he will be introducing sports betting legislation in the coming weeks.