New York Yankees closer Mariano Rivera injured his right knee during batting practice in Kansas City, Mo., on Thursday night and had to be carted off the field, raising questions about his return to the team this season.

Rivera's knee buckled when he fell awkwardly while chasing a fly ball at Kauffman Stadium during pregame warm-ups. Manager Joe Girardi and bullpen coach Mike Harkey ran over to assist the 12-time All-Star pitcher, who was taken off the field with his leg propped up. He was taken to a local hospital, and later reports said an MRI showed he suffered a torn ACL and a torn meniscus.

Rivera, 42, leads the league in saves, with 608 in his 18-year career. Before his injury, Rivera had indicated this might be his last season.