Found strange leg swelling

My cat was lying on his back, and as I was petting his legs I felt that one leg had an area of swelling, but the other leg did not. It's on the inside thigh, toward the rear of the leg. It's just slightly swollen, and soft - not firm.

He hasn't been favoring the leg or behaving strange. He didn't yelp when I touched it. No odd litter box problems or anything. I'm just perplexed! Should I call the veterinarian asap, or wait a few days and check again?

Cat is 9 yo and a bit overweight.

Hmmm that is perplexing. A call to the vet is in order whenever you want it to be as long as you don't go crazy with it and bother them all the time.

Does it seem to cause your kitty pain when you touch it-- watch facial expressions, not just noismaking-- , keeping in mind that cats are so very good at hiding pain? Does your cat go outside or playfight with any other indoor cats?

Are we talking like a mosquito bite or like a sprained ankle size sort of swelling?

And I have to know, does your cat like being pet on the legs? Zissou always thinks I'm trying to playfight with her if I touch her legs like that and feints a bite at me. It would be interesting to hear of a cat that liked it!