A. If your cat doesn't walk on that leg at all it is probably very painful. If he goes outside he probably hurt himself jumping, got into a car accident or got into a fight with another cat and has an abscess in the leg.
You should take him to the vet to rule out a fracture and other injuries, if it is an abscess he will need antibiotics and pain killers, if the pus is obvious it might need to be lanced and clean.
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