Objective: This study explored the association between concussion or musculoskeletal injuries, and the onset of mental health symptoms (MHS) in male professional rugby players over a 12-month period. Methods: Observational prospective cohort study with three measurements over a follow-up period of 12 months. At baseline, 573 participants provided informed consent. A total of 327 male professional rugby players (62% forwards, 38% backs) completed all follow-up assessments at baseline, 6 months and 12 months. The mean (±SD) age, height and weight of the participants at baseline was 25.9 (±4.4) years, 184.9 (±8.7) cm and 101.5 (±14.6) kg, respectively. Number of musculoskeletal injuries and number of confirmed concussions were assessed through single questions. Symptoms of distress, anxiety/depression, sleep disturbance, adverse alcohol use and eating disorders were assessed using validated questionnaires. Results: Professional rugby players who sustained a concussion within 12 months of baseline were more likely to develop MHS with ORs ranging from 1.5 (95% CI 1.0 to 2.1) for distress to 2.0 (1.2 to 3.6) for adverse alcohol use. Players who sustained a severe injury within 12 months of baseline were more likely to develop symptoms anxiety/depression with an OR of 1.5 (1.1 to 2.0). There was no significant association in both groups for other MHS. Conclusions: Rugby players who sustained concussion or severe injuries are up to two times more likely to develop symptoms of distress, adverse alcohol use or anxiety/depression.