Limping, angry cat.

My 4 year old, overweight, neutered cat started acting lethargic yesterday.  He would let me pet him but growled and hissed if I tried to pick him up and had difficulty jumping up on the bed.  I thought he was ill.  About three or four days ago he was playing with the new kitten, jumping on and off the bed, running up and down the stairs like he was five pounds lighter than he is.  Today, after sleeping on it for 12 hours, he can't put weight on his back right leg without hissing and growling.  He still let's me pet him.  His appetite is fine, breathing is normal.  This being a kinda, almost holiday all the vet hospitals in my area are closed.  I know it would be hard to say but I was wondering how severe this sounds and if a vet visit is even necessary. Thanks for your time.

Does he drag the leg when he walks or does he limp around?

He limps while walking very carefully.

He probably sprained the leg or knee. If it was broken you'd know it. I'd get him into a vet if he's still limping on Friday the holiday will be over then and vet offices should be open.

Will do, thanks!