Injuries are an inherent part of sports, and with increased training intensity and competition, they can become more frequent if athletes are not adequately prepared for such strain and stimulus. This paper describes the case of a young 20-year-old handball player who sought medical help after noticing symptoms of arm discoloration, swelling, pain and pressure. Upon examination and diagnosis, he was found to have deep vein thrombosis of the upper extremity and pulmonary embolism. He was admitted to the emergency intesive care unit for five days. He was treated with anticoagulant therapy and discharged home after the fifth day due to improved condition and reduced symptoms. Further more, therapy and follow-up were prescribed. The patient attended follow-up appointments approximately every six months until complete recanalization of the veins without the presence of thrombus residue was established. As his condition improved, his therapy was adjusted, and he gradually returned to sports activities. He started with low-intensity aerobic endurance activities in the form of continuous running for 30-45 minutes, 2-3 times per week, and on September 17, 2019 he partially joined handball practices. He started attending handball training sessions daily, participating in parts of the training focused on aerobic and anaerobic endurance, as well as exercises that did not require using his right arm. He gradually adapted to the workload to be as prepared as possible for a full return to handball training once he received clearance for complete participation. Further more, diagnostics revealed thoracic outlet syndrome as the cause of the thrombosis. During arm abduciton, the first rib and clavicle cause mehanical compression of subclavian vein, and due to the potential for recurrent thrombosis, surgical resection of the first rib was suggested. However, the patient chose to continue with conservative treatment and decided to not go on surgery. The patient actively returned to handball training and competition after two years and three months and remains active without symptoms of recurrent thrombosis.