This may only be a cyst, or a granuloma under the skin, totally benign. But it may not be. Check for symptoms, lethargy, lack of appetite, consider seeing the vet.
Of course you should, because it maybe a collection of puss caused by infection or any other contagious disease that may either harm your cat or even infect you . It may also be caused too by collection of blood under skin after a trauma so whenever you notice a nodule on your pet you have to visit the veterinary.
Did you just get the cat? Maybe you just feel her microchip, most cats are microchipped now. If the nodule is new and you did not feel it before, you should see a vet.
Any lumps or bumps big enough to be seen or felt are enough to cause alarm and a trip to the vet, as cats can develop feline versions of cancer and other life-threatening illnesses.
It depends on its size, location and your cat's overall reaction.If it is large in some important area and your cat behaves badly, you had better take it to doctor.
It depends on what kind of cat it is.If it is a very expensive genre, you should take it to the pet clinic at once, otherwise you do not need to worry that much and can inspect it for some most cases, this is very common and will not have much danger.
