An MRI will define whether it is chondromalacia and what stage it is. If the rest of his knee is fine, he can get some relief with a brace especially for chondromalacia that tends to secure the knee cap in position on the track which reduces a lot of the pain of walking. Any loose body tissue or debris that gets caught up in the mechanism will hurt until it is either removed surgically or on its own floating out from under the kneecap. I had the condition for about 20 years with flareups off and on, my brace always came in handy, called a chopat. Good luck.