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Mariano Rivera's career may have ended Thursday night, not while basking in the glow of adoring fans at Yankee Stadium, but in agonizing pain on the outfield grass before a few thousand fans in Kansas City.

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

Manager Joe Girardi revealed the diagnosis after the Yankees' 4-3 loss, the New York Post reported.

"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."

"He's going to be missed. There's no other way to put it," Derek Jeter said, according to MLB.com. "You can't replace him."

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    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.

    Speaking to reporters after the news, Rivera became emotional, having to wipe away tears as he paused to regather his composure.

    "It happened for a reason and you just have to live with it," he said.

    Asked whether his career could be over, the closer was non-committal. "I just have to live with this first," he said.

    Rivera said he would stay in Kansas City to support the team.

    Rivera, who routinely shags flies before games, was going after a ball in center field hit by newly called up outfielder Jayson Nix when the pitcher's knee appeared to give out. He stumbled then crashed into the wall. Rivera fell to the ground and could be seen grabbing his leg and writhing on the warning track dirt in pain, the Post reported.

    Near home plate, Alex Rodriguez, who was awaiting his turn in the bating cage, could be seen saying, "Oh, my God. Oh, my God," as he saw Rivera go down. Concerned teammates gathered around the reliever as the team's trainers and Girardi rushed out to tend to him.

    A cart was quickly summoned and Rivera, who was unable to put any weight on the leg or get on the cart without help, was lifted onto the vehicle by Girardi, bullpen coach Mike Harkey and reliever Rafael Soriano.

    The Associated Press and Newscore contributed to this report.