Debbie, I'm sorry to hear that Tubby's tail is going bald. Have you ever heard of stud tail? In my cat book it says that stud tail, like feline acne, is caused by over-secretion of the large sebaceous glands at the base of the tail. If infected, these areas may become pustulate. Commonest in toms, it can also occur in females and neuters of either sex.

It also shows a picture that looks very similar to Tubby's tail. It says that it usually doesn't bother the cat unless a secondary bacterial infection causes irritation. The solution is to regularly wash the area with a cat shampoo or rub it with an antiseptic such as chlorhexidine. Antibiotic treatment is also sometimes needed. I'd take him to see your vet just to make sure he's okay. I don't think you need to rush him to the vet so next Sat. should be okay. Goodluck and please keep us updated.