Murphy finally went to the vet yesterday. It turned out that he had another wound I didn’t know about in his arm pit. An abscess from there burst on Monday night and he is now stapled up and being given antibiotics twice a day. He seems quite well considering what happened to him.
The vet told me that cats don’t heal themselves and any sign of injury should be bought to the vet as their wounds fester really easily. Mea culpa. Please learn from my mistake.