Las Vegas sports books are worried about the Kansas City Royals and Houston Astros as the Major League Baseball season winds down.

The Royals are the consensus World Series favorites in Vegas. They are listed at 4-1 at the MGM sportsbook and have been attracting some significant wagers since early in the season.

"We took some pretty heavy action on the Royals the first weekend of the season," MGM vice president of race and sports Jay Rood said. "A gentleman bet them three times, at 18-1, 15-1 and 10-1, all the way down, between $25,000 and $30,000 a pop."

The Astros, after opening at 100-1, are down to 8-1 at MGM.

"We're on the hook for a seven-figure risk at 100-1 [on the Astros]," Rood said.