This is what our sycamore looks like these days.
It developed a fungus on some of the leaves that I tried to treat with neem oil. When that didn't help, and most of the leaves had fallen off, I did some research. We may have overwatered it, we may have planted the rootball too low.
Or maybe, this is just part of the normal cycle -- it is a deciduous tree after all. To be continued in the spring.