Abcess on the right foot. Me what to do.

Around 6 yrs ago my dad was diagnosed with the condition, had SMS jaipur neurologist take a look. They said that it had to be operated so we made up our mind to get it done but since it is lies exactly on a vein they said there could be some chances of complications as in like paralysis of the left foot so we returned from the O.T. untreated. He is a diabetic patient and has undergone 2 engioplasties. Blood pressure is always under control and insulin isn't required for sugar control. Untill now, the abcess is grown to some extent and it hurts if something touches it accidentally. There is no problem in walking or doing other stuff. In fact he walks two times a day for 6-10 km. Please tell me what to do.