A message left with Lohan's attorney was not immediately returned.
Lohan confirmed on her Twitter page last week that she failed a court-ordered drug and alcohol screening.
Lohan spent two weeks in jail this year after violating probation stemming from convictions involving her 2007 arrests for drug use and driving under the influence. She spent another 23 days undergoing rehabilitation at Ronald Reagan UCLA Medical Center.
Fox had threatened her with 30 days in jail for each probation violation. Fox must now decide whether to send her back to jail or back into treatment.