Rotator cuff injuries can be a big setback if not dealt with properly. For the most part Kraftkid is right. However, there are a multitude of special tests that can be used to diagnose the specific muscle that is injured. There are a group of four muscles that make up the cuff: supraspinatus, infraspinatus, teres minor, and subscapularis. Each muscle has a different action, therefore helping determine which muscle, or more likely, which tendon is involved. Best advice, if it doesnt get better, is to visit the doc and get a referal for PT to determine the exact muscular involvement. Until then stay off it and go eacy