Halep, a 31-year-old from Romania, announced in September she was taking the rest of this season off after having nose surgery to improve her breathing. She considered retiring early this year after a series of injuries, but then said she felt rejuvenated after teaming up in April with coach Patrick Mouratoglou, who used to work with Williams.
Seeded No. 7 at the US Open, Halep lost in the first round to Daria Snigur of Ukraine 6-2, 0-6, 6-4 on Aug. 30. It was the first tour-level win of Snigur's career.
Spokesmen for the US Tennis Association and Mouratoglou declined comment.
The ITIA said Halep tested positive in New York for the banned substance Roxadustat, a drug approved for medical use in the European Union to treat the symptoms of anaemia caused by chronic kidney failure.
Halep said she was told her test showed "an extremely low quantity."
According to the EU's medicines agency, which approved Roxadustat last year, it stimulates the body to produce more of the natural hormone erythropoietin, or EPO, which has long been a doping product favoured by cyclists and distance runners.
During a provisional suspension, a tennis player is ineligible to compete in, or attend, any sanctioned events.
Under the World Anti-Doing Code, Halep faces a ban of up to four years for a positive test for a substance like Roxadustat. Athletes can earn a reduction in their ban, likely to three years, if they quickly admit an offence and accept their sanction.
Tennis authorities will handle Halep's case and any ruling can be challenged by the World Anti-Doping Agency in an appeal to the Court of Arbitration for Sport.
"Today begins the hardest match of my life: a fight for the truth," Halep wrote Friday.