I'm a middle aged runner (jogger) training for a marathon, been running for many years injury-free, at about 40 mpw. About 2 weeks ago, I started to get a slight pain in my right ankle. On a 15 miler I recently did, I felt a slight niggle but this eased off but I continued running. Then on a run a few days later, I felt a pain on the inner side of my leg and my ankle pain worsened- this was very hard to run on. Took a rest week, went out for an easy 5k but still felt slight pain. More recently, I had a sports massage which has slightly helped, but I don't want to return too early and risk greater injury.
Been doing some XT on the bike since
What should I do? What could this be?