Early on. He has a chronic problem with one of his ears, if I remember right, from some concussion that happened before. It might be livable day to day but as an athlete you can't really function at a high level.
I think it was whiplash injury, not a concussion. It resulted in an internal ear problem, which gives him bad balance issues and dizzy spells. At least that's what I remember from the story.
It never seemed to get resolved. I have no hope it'll magically fix itself.