Autoimmune and coronavirus

So I have a small business and I have a worked who is 25 and had childhood leukemia. He’s is remission and has been for over 10 years. He’s trying to get off work because he is afraid of getting corona virus because of this. His dr won’t sign him a note to leave work. I’m filling in and I don’t have much experience with this so what do I do? I know if you have diabetes you shouldn’t be around people but he’s cured from cancer. Any advise