Skeletal muscle metastasis from lung cancer is a rare manifestation that often presents significant diagnostic challenges in clinical practice. We report the case of a 58-year-old man with a 25-pack-year smoking history who was diagnosed with lung squamous cell carcinoma following evaluation for persistent cough. Initial staging revealed no evidence of distant metastasis, and the patient was treated with systemic chemotherapy, which resulted in stable disease. Nine months later, the patient presented with a gradually enlarging and painful mass in the right gluteal region. Magnetic resonance imaging revealed a cystic intramuscular lesion with mural nodular components within the gluteus maximus muscle. Ultrasound-guided biopsy confirmed metastatic squamous cell carcinoma morphologically consistent with the primary lung tumor. The patient subsequently received second-line chemotherapy.