Tennis star Novak Djokovic was injured during an accident at the Italian Open, RadarOnline.com has learned. While signing autographs on Friday afternoon, a metal water bottle fell from the crowd and struck the Serbian tennis star in the head, causing him to drop to the ground. After his second-round win in the Italian Open, Djokovic stopped to sign autographs for fans. Moments later, the water bottle appeared to fall from the stands and hit the tennis star in the head. Djokovic immediately clutched his head and dropped to the ground. Security guards quickly surrounded the tennis player and esc…