Hi, it looks to me like it COULD be ring worm, which is a fungal infection. I hope that's what's wrong with your cat, but I wouldn't assume. Bring your cat to the vet and get a definite answer. If it turns out to be ring worm, he will give you a formula that is safe for cats that will heal him up in no time. The over the counter products that treat human fungal infections are not safe and can be poisonous for cats, so do not use them.
Check out these pics to see if this could be your cats issue.
https://images.search.yahoo.com/search/images;_ylt=AwrBTz4xtUVTknYAkbVXNyoA;_ylu=X3oDMTB0NDAwYXNwBHNlYwNzYwRjb2xvA2JmMQR2dGlkA1NNRTQwMV8x?_adv_prop=image&fr=yfp-t-901&va=ringworm+cats
Hello there,
I agree with Opus88's comments. Please bring your kitty to a certified
vet as soon as possible so a vet can look at your fur baby. I wish you
and your cat the best of luck as well. Eve ( mother of Sammy the cat)
sorry I am having a hard time seeing exactly what this is.....I do encourage you to have any lumps, bumps or sores of any kind seen by a Vet asap...this could be a tumor, we cannot diagnosis anything on here this has to be done by a Vet and a good visual exam....good luck:)