Lumps on back of hind leg

My fiancé and I are a bit worried about Buddy. We were snuggling him and noticed 3 lumps on the backside of his left leg. All progressive in size. (Large, Medium, Small). I'm hoping it's nothing to worry about but I am concerned about it. Does anyone know what this is?

No idea, and you won't get a definitive answer from anyone online. Some guesses I could throw out include bug bites, abscesses/infections, a physical deformity, cysts, cancer....on and on. 

It's best to have a vet check out the lumps and determine what they are. You'll find numerous suggestions (and scare stories) on what the lumps may be online but only a vet will be able to physically examine the cat and determine what the lumps are.