Stress fractures are frequently underdiagnosed and undertreated despite being common in sports. Early diagnosis is crucial; therefore, a high index of clinical suspicion is required. Complementary examinations are essential for diagnosis and follow-up. The authors report a clinical case of a young adult triathlon athlete referring mechanical pain in the rear left foot, with 2 weeks’ progression. An earlier increase in daily training intensity was recorded. Complementary examinations confirmed a calcaneal fatigue fracture. Immobilization and no weight bearing were introduced for an initial period of 4 weeks, and the rehabilitation process was started. Progressive weight bearing was introduced between fourth and eighth weeks. Sports activity started at the 12th week. Boundaries to sports activity were eliminated by the 24th week, without pain or functional limitation. Repetitive overload to the heel and intense axial weight bearing in association to repetitive concentric/eccentric gastrocnemius contraction are related to calcaneal stress fracture, the second most common stress fracture in the foot. Calcaneal stress fractures can be adequately treated with activity modification, without casting or surgical intervention. When in the presence of bilateral stress fractures, metabolic and nutritional issues must be considered. The case report highlights the importance of sports medicine examination for detecting intrinsic and extrinsic fatigue fracture risk factors.