If you asked this earlier in the season, I would suggest that your tortoise is getting ready to hibernate, but at this time of year, the gut should be completely empty and the tortoise should already be nodding off.
In general, when a tortoise or turtle doesn't eat, it is because it is too chilly. Provide a basking spot where the temperature is about 80 degrees. The tortoise will need to be able to get cooler as well, but do try the heat treatment first. If that doesn't work, see a vet because there could be something else you can't see.
