Groin pain is a cause of mobility impairment, and its diverse presentation can make the diagnosis difficult. Quadratus femoris muscle tendinopathy is a poorly described etiology, but its diagnosis is important for the success of the therapeutic program. The authors present the case of an 18-year-old woman who complained of chronic pain in the left inguinal region due to regular ballet practice. Physical examination revealed restriction in the left hip medial rotation. Ultrasound and radiographic studies were normal. Magnetic resonance imaging showed asymmetry in the signal intensity of the quadratus femoris muscle. The patient improved significantly after a rehabilitation program that included quadratus femoris muscle-specific exercises. Diagnostic accuracy and an understanding of segmental biomechanics ensure greater effectiveness in the therapeutic approach.