In this image taken from video, New York Yankees manager Joe Girardi, right, helps Mariano Rivera, top center, after Rivera twisted his right knee shagging fly balls during batting practice before a baseball game with the Kansas City Royals, Thursday, May 3, 2012, in Kansas City, Mo. The Yankees closer was carted off the field and sent for further tests. (AP Photo/YES Network)

Photo by: Uncredited

In this image taken from video, New York Yankees manager Joe Girardi, right, helps Mariano Rivera, top center, after Rivera twisted his right knee shagging fly balls during batting practice before a baseball game with the Kansas City Royals, Thursday, May 3, 2012, in Kansas City, Mo. The Yankees closer was carted off the field and sent for further tests. (AP Photo/YES Network)