My cat seems to have a rash....(please read)?

Question

I just noticed a quit progressive rash on my cats left hind leg. It's almost near his private area. He is missing hair there (as if he was shaved, but no one shaved him). It is also a bit red and irritated. I checked his fur for fleas, but I saw nothing. I have not noticed him messing in that area, so I am clueless!! I feel bad because all the local veterinarians are closed until Tuesday (monday being a holiday). Any ideas what it could be? Is there anything I can do until I can get him to the vet? My fiance suggested we try a flea bath in the meantime. We use the same brand of kitty litter that we always use. (tidy cats) Any suggestions would be greatly appreciated.