Background: Sport-related mild traumatic brain injury (TBI) is a serious trauma that could impair brain function of an injured athlete. Treatment solutions for mild TBI typically concentrate on complete rest, while non-traditional therapeutic options remain largely ineffective. Molecular hydrogen (H 2 ) is an innovative neuroprotective agent that can easily reach the brain, yet no data are available concerning its value as a first-aid intervention after a mild TBI. Case report: This case report demonstrates the efficacy and safety of a hydrogen-producing dissolving tablet administered buccally during the first 24 hours post-injury in a professional soccer player who suffered a mild TBI. The patient received a formulated dosage of hydrogen every 2 hours, with the first intervention given immediately after an initial examination (~ 15 min after the injury). The overall score for Sport Concussion Assessment Tool 2 (SCAT2), a standardized method of evaluating injured athletes for concussion, increased from 68 points (severe disruption) at baseline to 84 points (mild disruption) at 24-h follow-up. The patient reported no side effects of hydrogen intervention. Conclusions: This case has demonstrated that intensive consecutive therapy with oral transmucosal hydrogen formulation is a beneficial strategy with regard to the reduction of presence and severity of symptoms of sport-related mild TBI.