“ER or not?”

My 83-year-old Dad has weeping leg syndrome on his left leg on his calf. Dad will have an appointment (had to wait 4 weeks for appt) on 9/8. He went to Urgent Care 2 weeks ago and gave him a shot in the butt and antibiotics to take for 10 days to prevent infection. Leg seem to improve some. I did not know about this whole thing until last week and went to visit Dad Saturday. Saw his leg. Open sores. It is purple and swollen from the knee down to his toes. He had DVT years ago on his lower left leg. What do you make of this? I have not seen Dad or talked to my parents since Saturday night. I am concerned. Should he wait until 9/8 for his doctor's appointment It is crazy that Dad had to wait 4 weeks for his appointment. He is almost 84 years old.