It is likely just granulation tissue. Granulation tissue is a normal part of wound healing in the lower legs of horses. It grows from the edges of the wound until it meets in the center and then pulls the edges of the wound together and skin can then form.
Proud flesh is an overgrowth of granulation tissue. Most people mistake healthy granulation tissue for proud flesh and in trying to get rid of it actually prolong healing of the wound and increase the amount of scar tissue which will form.
Your best bet is to clean the wound out well with plenty of water, fluorhexadine and make sure the hair is toweled off, then with a non stick pad from any drug store over the wound, carefully stable bandage the leg (it is not necessary to do any of the other ones - this is an old wives tale). Try to change the bandage every day if it is still draining, but the main purpose is just to keep the wound clean and allow the granulation tissue to grow undisturbed. With a lot of big wounds on the lower limbs of horses (life threateningly large - down to the bone, etc..) they are actually casted for weeks without being changed. And recent studies have shown that clean wounds, left covered without any ointments and junk on them heal faster.
This would be my advice. If it is a large wound and you are concerned, I would contact a vet.
They say money doesn't buy happiness -- well happiness doesn't buy horses!