An MRI revealed the extent of the injury, suffered Saturday night in the club's penultimate Catcus League game on Saturday night.
Cotts, 31, felt something as he threw a wild pitch to the final batter he faced in his lone inning of work in that game. He was one of just two remaining left-handed pitchers on the roster at that time. The next morning, Robbie Ross was named to the roster as the club's only left-handed reliever.
Cotts hasn't pitched in a major league game since 2009 because of injuries. He had Tommy John surgery that season, missing all of 2010. He had surgery to repair a torn labrum in his hip and got an infection from it. That required three more surgeries and he said earlier in camp that it was the hip, not Tommy John, that was keeping teams from calling him to give him a shot.
Cotts started in minor league camp this spring, but quickly impressed coaches in his bullpen sessions and intrasquad games and was moved to major league camp. He pitched consistently all spring.