Take your cat to the vet if you notice the lump is getting larger, especially if it continues to grow 1 month after the injection. [substeps] The lump will likely be fairly hard and not move around that easily.
[header] How to diagnose and treat feline injection site sarcoma [title] Watch for a growing lump. [step] A small lump is normal when a cat receives an injection. However, if it grows bigger over time, that is cause for concern.