I have a small lump under the skin on my left lateral malleolus ...peroneal tendon area. Sometimes it isn t painful but if I push on it a bit or exercise, it starts to be a bit tender. Several months ago, my ankle swelled up and was sore and puffy for a couple weeks. When the swelling went down, this small lump is what was left. Not sure if it s scar tissue , if I move my ankle around, the size of the lump seems to contract or expand.