A healthy 20-year-old Division I track athlete participated in out-of-season practice and experienced inflammation on mid-lateral aspect of his right calcaneus. The patient modified his weekly training program, and a magnetic resonance imaging revealed the presence of an accessory peroneus quartus. This muscle is present in around 5.2% of the population. The pathological symptoms cause pain, snapping, and synovitis. Literature shows a higher prevalence of the accessory peroneus quartus muscle in males of European/American descent and in the right lower leg. Symptoms include peroneal tears, decrease in range of motion, and pain of the ankle and foot.