Yankees closer Mariano Rivera suffered a torn ACL in his right knee shagging fly balls before Thursday night's game against the Royals in Kansas City.

Manager Joe Girardi revealed the diagnosis after the Yankees' 4-3 loss.

"That's about as bad as it gets," Girardi said. "You lose a Hall of Famer it changes [the bullpen] a lot. We like the depth of our bullpen and it just got a little bit shorter. We'll have to find a way to get through it."

Rivera had an MRI exam, and Girardi said Royals doctors saw Rivera had torn the ligament. He will be re-examined in New York by Yankees doctors for confirmation.

The injury would end Rivera's season and possibly the career of the 42-year-old all-time saves leader.