Is it a psychological thing?

ok, well my uncle is convinced that his body is in terrible condition and that if he stops working out he will mess his body up. He says that he needs his body to regenerate itself. He refuses to get a job and refuses to do much for himself. He relies on my grandparents for housing and food and has no ambition in life. He thinks that he is not able to hold a job with his physical condition even though he is muscular and fit. I want to know if this is some kind of psychological condition or something because im worried that he may never want to do anything with his life ever. And when the time comes and my grandparents pass away he will have no where to live and nobody to provide for him. What the hell is it? I seriously am worried that he is mentally ill.