Looking closely at the photo, I think that this is simply a robin that has lost rather a lot of feathers from its head. The pale patches appear to be simply skin with no feathers. The feathers are quite fluffed out, so emphasising the rather small robin inside! Could be disease, or perhaps caught by a cat and escaped. Look at the top of the head and you can see isolated feathers.
I did consider whether it was just a bald patch but I can see white feathers around the white area, particularly at the top, suggesting leucism (to me). However, I must admit it's not the greatest of photos.