The 5-year-old boy was reported missing after McCready took him from her father's home on Tuesday. Her mother and father are divorced.
McCready's mother has custody of the boy.
A judge ruled she must return him today or risk an arrest warrant.
McCready told The Associated Press she probably won't be able to return the boy because she's nearly seven months pregnant with twins.
The singer also said that she and her mother have had a long custody battle in Florida over Zander. Her mother was awarded guardianship in 2007.
That battle spilled into the public eye this week when the Florida Department of Children and Families said a missing person report was filed with police after McCready took her son from her father's home.
McCready was able to visit with the boy there under a court order and the 36-year-old singer said she had spent much of the past month with her son at the home.
McCready alleges that her son suffered abuse while living at her mother's home and that is one of the reasons why she left with the boy last week.
The singer told AP that she is suing her mother and a tabloid newspaper for libel in a Palm Beach County court.
The Associated Press contributed to this report.