First baseman Sean Casey will be out of the Pittsburgh Pirates' lineup for six to eight weeks with two fractures in his left lower back. Casey, the Pirates' highest-paid player, was injured during Friday night's game against the Cubs while he was stretching for a throw. As John Mabry was running out an infield single in the third inning, he stumbled crossing the bag and clipped Casey with his hip or left elbow. Casey took several strides toward the pitcher's mound with the ball before dropping to his knees in obvious pain. He was assisted off the field and needed help getting to the clubhouse before being taken to a hospital for tests. "When he and Mabry collided, I knew there was something wrong. I knew there was something more than having the wind knocked out of him," manager Jim Tracy said Saturday. "He was feeling shooting pain down his lower back and three times he tried to stand up and couldn't."