Large, red, oval shaped swelling on cat’s leg

Hello and thank you so much in advance for any advice. This red swelling has appeared very quickly on my cat’s leg. I was with him a few hours ago and didn’t see anything but now it is very prominent. He seems fairly well and relaxed but I am very worried about what the cause may be. He finds vet trips very stressful so wondering if I might get some useful advice here before deciding whether the emergency out of hours vet is necessary. 

Hello!  If considering the out of hours vet, always just ring them up - they are usually quite good at triage, the art of working out how quickly a case should be seen.  They are also, unlike us, your vets and advice from your vet who knows the patient and can speak to you, will always be better than emergency advice from an online vet who may check periodically but is not 'on call.'

Anyway, you asked about a red painful swelling that has come up very fast, and I wonder about an abscess, traumatic wounds, unusual parasites.  However, tumours, foreign body reactions, insect or spider bites and so on would also make the differentials list.   Best of luck and please do let us know what is found.

Thank you very much for the opinion. We took him to the vets today, and her opinion was that this was most likely infected wounds caused by another cat, but also could be a fungal infection, and he received a shot of antibiotics and wound cleaning which we’ll continue with, as well as some skin cultures. He is now home and sadly having some trouble adjusting to the collar the vet attached to prevent him from licking his wounds. We don’t want to let him outside as we are worried he may disappear (he did this once before after a vet visit) or not be able to manage easily with the collar (I had to detach his foot from it a couple of times when he got it stuck trying to claw the collar off). But he is very stressed indoors and not using the litter tray (he is not accustomed to it) so we will have to reassess tomorrow.   Thanks again for the advice.

I'm glad they're also wondering about possible abscesses / infected wounds.  I wish that there was an easy remedy to suggest regarding the collar dilemma, but it's tricky for outdoor cats.  I notice that this is an under-represented topic in our blog, although I found a brief mention here:    https://vethelpdirect.com/vetblog/2022/04/10/why-does-my-cat-have-a-bald-spot/#h-cat-bite-abscesses    I will pass this on to the blog-writing team.

Regarding collars, they can be tricky for cats.  It may help, if you haven't already, to choose a soft / clear one and have it fitted for size, as they tend to be better tolerated this way.   There is a balance to be found between licking vs the damage or stress caused by a collar and sometimes, with ample appropriate pain relief, the need to lick an abscess / infected lump can be reduced sufficiently to favour the balance that way.   Best of luck with it and do let us know how the story ends.

The wounds are healing really well such that today we decided to take off the collar and he is so over the moon! Having said that he calmed down a lot after the first couple of hours of wearing the collar and having to stay inside and adjusted really well back to the using the litter tray and it gave the wounds time to dry out and start healing so I think it was the right thing to do.   Thank you very much for the advice.