So, I don't see a picture. Absolutely, someone with diabetes if they have skin issues on their feet needs to show them to their doctor. Diabetics can have complications and they can get serious. If this is a diabetic food ulcer, which happens to about 15 percent of people with diabetes, you need to make sure to care for it properly. https://www.apma.org/diabeticwoundcare Pressure, trauma, irritation to the skin, etc. can end up being a serious problem with someone that has diabetes and especially insulin dependent diabetes. Here's another article talking about it. https://www.webmd.com/diabetes/features/diabetes-wounds-caring-sores#1 I am not trying to be an alarmist but with his pre existing condition, you should get this checked out and guidance for how to care for it.