Exclusion and bypass for penetrating vascular injury remains the gold standard. Persistent hemorrhage via retrograde perfusion of the injured vessel by collateral vessels is rare and may, therefore, be overlooked as a cause of postoperative hemorrhage following bypass for vascular injury. We report a case of a 49-year-old male who presented to our institution 2 weeks following a bypass graft of his popliteal artery after sustaining a gunshot wound to the vessel. His ongoing complaints of pain and pressure in the popliteal fossa were found to be related to persistent collateral perfusion of the injured segment of his proximal popliteal artery. His symptoms resolved completely following coil embolization of the injured native artery. While quite rare in clinical practice, the pathophysiology of this case is analogous to persistent perfusion of the aneurysm sac following open abdominal aortic aneurysm repair or bypass and exclusion of a popliteal artery. In the setting of bypass grafting for vascular trauma, postoperative hemorrhage or compressive symptoms should prompt a complete evaluation for a potentially missed patent collateral vessel.