A patient with advanced rectal cancer (T3cN2bM0) refused the recommended neoadjuvant chemoradiotherapy and underwent laparoscopic radical resection. Three months after surgery, he developed an isolated metastasis to the left peroneus longus, which presented as a painful mass. 18F-FDG PET/CT scan showed the hypermetabolic nature of the mass, suggesting malignancy. Histopathological examination confirmed skeletal muscle metastasis from rectal adenocarcinoma. Solitary skeletal muscle metastases from rectal cancer are exceptionally rare and have a poor prognosis without established treatments. The patient was treated with a combination of surgical resection and systemic chemotherapy. During the 30-month follow-up, he did not experience local recurrence or further metastases. The case highlights the need for clinical attention to rare skeletal muscle metastases and individualized treatment.