New York Yankees closer Mariano Rivera suffered a torn ACL while shagging fly balls before the Yankees game against the Kansas City Royals on Thursday. Rivera was leaping for a ball hit by Jayson Nix when he fell on the warning track. Rivera was noticeably in pain as he was grimacing and rubbing his face. Rivera regularly fields fly balls during practice to stay in shape. Rivera was carted off the field and needed help to walk into the Yankees' clubhouse. During the game, he was sent to Kansas University Med-West Hospital for an MRI. Royals trainer Vincent Key diagnosed the torn ACL after examining Rivera's MRI. Yankees manager Joe Girardi has said that he is leaning towards naming David Robertson as Rivera's replacement and Rafael Soriano as Robertson's setup man.