I don't think so. The employer has the right to terminate employment without cause.
..............except if it violates the American Disability Act.
My ex-wife had this same situation arise at her insurance office. They procrastinated about firing a lazy woman who arrived late, left early, took long lunches and didn’t work very hard. One day she announced that she had ovarian cancer, I believe it was. Until she was in complete remission they had to keep her on.