Background: Vascular injury after total knee arthroplasty (TKA) is rare but may be limb-threatening. Popliteal artery branch pseudoaneurysm is an uncommon complication that can present with nonspecific symptoms, potentially mimicking postoperative hematoma, infection, or deep venous thrombosis (DVT). Case presentation: A 79-year-old man underwent primary left TKA for advanced osteoarthritis (OA). Seven months later, he sustained a low-energy fall closed reduction and bracing were implemented. Due to recurrent episodes of instability with spontaneous self-reduction, a constrained revision TKA (R-TKA) was performed. Eighteen days after revision, the patient was readmitted because of persistent pain-related functional impairment. Duplex Doppler ultrasonography revealed a partially thrombosed pseudoaneurysm measuring 33 × 37 mm arising from a popliteal/genicular branch. Computed tomography angiography (CTA) confirmed a partially thrombosed pseudoaneurysm with a contrast-filled component within a larger periarticular fluid collection. This suggested a second, smaller pseudoaneurysm along the feeding vessel; hemarthrosis and soft-tissue edema were also present. After multidisciplinary evaluation, selective catheter angiography via left common femoral access was performed, and the injured branch was occluded using coil embolization combined with n-butyl cyanoacrylate tissue adhesive. Completion angiography demonstrated successful exclusion of the pseudoaneurysm without complications. Conclusions: Delayed pseudoaneurysm of a popliteal artery branch should be considered after revision TKA in patients with atypical swelling, hemarthrosis, or disproportionate pain. Duplex ultrasound and CTA are complementary diagnostic tools, and endovascular embolization provides a minimally invasive, effective, and low-morbidity treatment option when the lesion involves a branch vessel.