Subtenon's block is commonly used to achieve akinesia, analgesia, and anesthesia for ophthalmic surgeries. This case study detailed a rare hypersensitivity report in a 65-year-old female who had underwent manual small incision cataract surgery under subtenon's anesthesia (STA) in the left eye. On postoperative day 1, she presented with acute onset proptosis, periorbital edema, conjunctival chemosis, and restriction of extraocular movements. The pupillary reaction and dilated fundus examination were normal. A differential diagnosis of orbital cellulitis, Mucormycosis, and hyaluronidase hypersensitivity (HH) was considered. Since the patient was afebrile, and pupillary reactions, ENT, neurological, and fundus examination were normal, the diagnosis was narrowed down to delayed HH. The patient was managed with a 1 cc IV injection of dexamethasone once a day for 3 days, along with routine postoperative drugs. As per detailed literature review, this is probably a second case report of delayed HH post-STA.