Knot

I just recently discovered a knoot the size of a golf ball on my horse's leg where the leg bends today. It seems to be bothering him, because before I discovered it, I tried to get him to trot and he began to trot/limp. It isn't hot. Is there anything I can do to help it heal?

You need to get a vet out to look at it. Who knows what it is, we certainly can't help.