Britney Spears failed to attend a court-ordered deposition after telling her ex-husband's lawyer that she was feeling unwell.
Spears has visitation rights regarding her sons
Ms Spears was due to arrive at the office of Kevin Federline's lawyer, Mark Vincent Kaplan, on Wednesday.
"She's going to show at a later date," Mr Kaplan said, adding that he may ask for "certain relief" from the court due to Spears' non-attendance.
Ms Spears and Mr Federline are battling over custody of their two young sons.
Mr Federline was granted full custody of Sean Preston, aged two, and one-year-old Jayden James in October.
A deposition is a statement taken under oath, usually in a lawyer's office.
A court ruled last month that Ms Spears must provide a working telephone number so she can be reached for drug testing.
Mr Kevin Federline's lawyer told the court there had been 14 requests for drug testing and she failed to respond to eight of them.
But Ms Spears' lawyer argued the singer had not responded within the ordered time frame because she was sleeping.