Thursday? November? PA? Mine keep for weeks (in the fridge, though).
I have often used old mushy potatoes. It is no big deal if consistency is not the top issue. I would certainly not use it for baking, though. Stews, mashed potatoes, soups are fine. Fries, baking, gnocchi are not.
Hard to do stews with just one potato, though.
The best way to see how it is faring is cutting it and checking for dark or graying areas.