MSFinals-2695

A 50-year-old man visits his GP complaining of increasing pain in one leg over the past 6 months. He also reports mild weakness in the affected leg during any activity. The pain travels down the back of his left leg and worsens when walking, causing him to stop and rest frequently. However, the pain improves when he sits or crouches down. The patient has no history of smoking or cardiovascular issues and has a body mass index of 19.0 kg/m2. There are no abnormalities found during back and neurological examinations. What is the most probable diagnosis?