Can HR or Manager of a company force you to resign because you cannot come to work because of medical problem?

I need some advice. I am suffering from a disease since I was 16 and have an infection in my stomach. I had an operation 4 years back and lost one of my kidneys. Since then I was fine. But from the past one month, it started paining again and I could not go to work. I went to doctor and found out that the infection has increased to my liver. I need to do the scans and only then my doctor could say anything. I kept my manager informed about it. Now he is telling me to resign and rejoin the company. I spoke to the HR and he told me the same thing. I know I wont be getting any salary as my leaves are already over but what I want them to do is to let me join in a month’s time. I want to know that can a company (HP in this case) force an employee to resign because she is undergoing a serious medical problem. I need some advice about what I need to do.