Conor McGregor just underwent successful 3.5 hour surgery in Los Angeles ... where doctors inserted a rod in his tibia and plates and screws in his fibula, sources tell TMZ Sports.
McGregor -- who suffered the gruesome lower leg injury during his fight with Dustin Poirier at UFC 264 -- was transported to Cedars-Sinai hospital in Los Angeles where he underwent the procedure this afternoon.
Sources tell us Conor had a intramedullary rod inserted in the tibia .