There are many microvascular and macrovascular complications regarding uncontrolled diabetes mellitus (DM). Among them, diabetes myonecrosis is one of the complications but rarely seen in the uncontrolled DM patient population. Here, we present a rare case of DM myonecrosis in a patient with elevated hemoglobin A1c (HbA1c) of 18.2% and discuss the literature review of diabetes myonecrosis. A 48-year-old male with hypertension and uncontrolled type 2 diabetes mellitus (T2DM) with hemoglobin A1c of 18.2% presented with progressive swelling and pain in the right thigh for two days. Physical examination demonstrated swollen and tense tender right thigh with a circumference five inches larger than the left. Computed tomography (CT) and magnetic resonance imaging (MRI) results revealed severe myositis of the right leg, likely myonecrosis, and associated fascial edema/fasciitis. The patient was also complicated with diffuse anasarca, which was corrected with albumin transfusion and furosemide. Aspirin and lisinopril were also started for antithrombotic and cardioprotective effects. The right thigh swelling improved, and the patient could ambulate with supportive measures and regular physical therapy (PT). He was discharged home after 45 days of hospitalization. Diabetic myonecrosis is a rare condition and hence is underdiagnosed. In patients with uncontrolled diabetes, especially with diabetic complications, physicians should have high clinical suspicion to diagnose diabetic myonecrosis when patients present with an acute unilateral painful swollen limb. Our case highlights the complicated course of diabetes myonecrosis with anasarca, improved with supportive measures.