why is my cat is limping?

The abcess that your cat once had may not have completely cleared up. However, if it has, your cat is still feeling a little discomfort due the infection that was in his leg. Just continue to monitor your cat and if the condition does not get better, take him/her to tge vet.

Does his leg look bigger than the other one? If so, it could be swollen. Does the leg seem loose? If you are able to detect a click in his leg, it's a sign of a torn meniscus. Has he fallen from someplace high lately? Or at all? If so, and if you find all of this to be true, it could be a ruptured cruciate (torn knee ligament)

I found this:

Ruptured Cruciate (Torn Knee Ligament)

The knee is stabilized by two internal cruciate ligaments that cross one another in the middle of the knee joint. A pad of cartilage (the meniscus) sits between the bones of the joint as padding. The knee ligaments may rupture and the meniscus can tear after a car accident or a fall from a height. Signs of injury include joint swelling, pain on flexing and extending the knee, and looseness of the joint. You may be able to detect a click in the joint, which is a sign of a torn meniscus.

Treatment: Immediate surgical repair of a badly damaged knee joint is the treatment of choice. A mild injury, perhaps limited to the meniscus, can be treated with cage confinement for three to five weeks to rest the joint and allow it to heal by itself. If lameness persists, surgery should be considered. TTouch (a trademarked form of physical therapy) techniques, massage, and physical therapy, even hydrotherapy, can help the healing process for a cat with a ruptured cruciate.

Take your cat to the vet do you want him to keep limping. He can probably hurt it worse.

might of broke its leg cats feel much less pain then human

take it to the vet before it becomes too late.