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My cat has a painful lump under his skin and is lethargic. What is it?

Updated On September 23rd, 2025

Pet's info: Cat | American Shorthair | Male | unneutered | 1 year old | 15 lbs

My cat has developed a large soft lump underneath his skin and fur (about 3" long 1 & 1/2" - 2" wide). It hurts him when it's touched. He's still eating and drinking and moving around the room off and on but it's visible that he's lethargic and weak. What could it most likely be?

4 Answers

Most Helpful Answer

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Answered By Lauren Jones VMD

Veterinarian

Published on April 14th, 2017

Monkey's skin lesion could be due to an abscessed wound or a benign or malignant mass. An abscess is most likely given that he is also lethargic. A vet should examine Monkey to evaluate this lesion, and if an abscess is diagnosed, it will need to be drained and flushed. Antibiotics would also be needed for an abscess. I hope he's feeling better soon!

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    Answered By Andrea M. Brodie, DVM

    Veterinarian

    Published on

    If your kitty is an inside-outside cat he may have gotten into a fight and this could be a cat fight abscess. This could also be an insect or spider bite. I suggest you take Monkey to a veterinarian right away for an exam. If it is an abscess your vet will lance it and prescribe antibiotics. Depending on the diagnosis he may also need to get pain medication and antihistamines.

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    Answered By Dr. Strydom, DVM

    Veterinarian

    Published on May 30th, 2019

    You are correct. This sounds like an abscess. He will need oral antibiotics and sometimes surgery to open the abscess in order for this to heal. It is not something you will be able to treat at home. I suggest you get him to the vet for treatment. Best wishes.

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    Answered By Lauren Jones VMD

    Veterinarian

    Published on October 23rd, 2021

    Cats can develop lumps on their backs for a number of different reasons. One of the main culprits of soft, squishy lumps under the skin - particularly in cats that are around other animals or go outside - is an abscessed bite wound. Abscesses are basically pockets of infection and require veterinary treatment in order to properly drain and flush them, and to prescribe antibiotics. I'd recommend taking Leo to his vet for evaluation to get to the bottom of this lesion so that treatment can be started promptly. I hope that he feels better soon! https://www.petcoach.co/cat/condition/abscesses/

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