I have an English walnut sapling that grows vigorously all summer, but at the beginning of Fall the leaves dry up and fall. It has been two years now. Is that a problem with the tree?
According to a couple of different sources, walnut trees are among the first to lose their leaves. (And among the last to leaf out in spring.) Those pages are discussing Juglans nigra (Black walnut), but as far as I can tell Juglans regia (English walnut) behaves the same way.
There is a fungus, walnut anthracnose, that can cause early leaf drop. You didn't mention symptoms of this, and you'd have seen leaves drop back in August. Also, English walnut is less susceptible.
So what you are seeing is normal unless you have the spots on the leaves and fruit as seen in the photos in the link above.
Walnut is deciduous, i.e. it is meant to lose its leaves in Autumn (Fall).
I don't know where you are located but if the climate and seasons are slightly different from its native habitat (originally Balkans-Himalayas) then it may lose it's leaves slightly earlier or later than in its native habitat.