We present a case of a soccer player who sustained a lateral ankle fracture and the associated proximal anterolateral tibiofibular joint instability (Maisonneuve injury) was overlooked. After a non-contact injury the (incomplete) diagnosis of a lateral malleolar fracture (type Weber B, AO 44-B1) was made and the patient was surgically treated with open reduction and internal fixation including a distal syndesmosis screw. After removal of the syndesmosis screw (six weeks after surgery) the patient suffered from activity-related pain around the fibular head. After thorough clinical and radiologic examination, temporary screw transfixation of the fibular head and capsular repair under meticulous fluoroscopic control of fibular rotation helped to restore patient's sport activity level. This case report emphasizes the importance of precise clinical examination for detection of a proximal tibiofibular joint instability. Restoration of a well functioning and stable proximal tibiofibular joint may be difficult to achieve in previously operated and missed instabilities.