We report the first case of axillary nerve neuropathy in an adult secondary to shoulder septic arthritis with abscess formation. Prompt surgical drainage, lavage, and targeted antibiotic therapy led to full recovery. This case also highlights the risks of intra-articular injections, particularly in immunocompromised patients, and underscores the importance of maintaining a high index of suspicion for septic arthritis in this population, even when the classic signs are absent.