Suggest Treatment For Swelling And Pus Formation In The Foot Due To A Terrible Infection

I have a friend whose foot was infected real bad. I took him to the ER and they prescribed daily visits to Wound Care. After this regimen showed results, he stopped going. Now, 3 weeks later, the foot has swollen up, started to ooze pus and his middle toe is turning black. He is asking me about gangrene and I m thinking necrosis of some sort, which the Web tells me is pretty much the first step in gangrene. What do you think is going on? What do you think this is? Obv he needs to go back to hospital. We just wanted some initial idea of what it could be; I understand your diagnostic opinion would be based on only what I ve told you and it could be something else. A general idea is what we re looking for.