A 24-year-old female patient who had a type A influenza virus infection prior to admission visited our hospital complaining of a fever and right sternoclavicular pain. Blood culture was positive for penicillin-sensitive Streptococcus pneumoniae (pneumococcus). Magnetic resonance imaging of the right sternoclavicular joint (SCJ) showed a high signal intensity area on the diffusion-weighted images. Consequently, the patient was diagnosed with septic arthritis due to invasive pneumococcus. When a patient complains of gradually increasing chest pain after an influenza virus infection, SCJ septic arthritis should be considered in the differential diagnosis.