Wrongful Termination?

First I live in California. Went to the doctor on Thursday July 23rd. He put me out of work for three weeks. Faxed over the doctor’s note into work, I get a call from the owner insisting I still come into work the next day for a few hours. I explained my doctor put me out and I was told not to go in. Then Tuesday two employees I work with call me at home to tell me the company is interviewing for my position. So I haven’t been told I am terminated, I expect that when I return. But my question is, is it lawful for them to fill my position after being put on disability by my doctor?

Thank you for any help you can provide.