World 400m champion Salwa Eid Naser missed four anti-doping tests rather than the three she claimed, says the Athletics Integrity Unit.
The Bahraini, 22, ran 48.14 seconds – the third-fastest time in history – to claim the world title in Doha in 2019.
But the AIU says there was a fourth whereabouts failure in January 2020.
She has been provisionally suspended.
In a statement, the AIU said: “The investigation into Ms Naser’s three whereabouts failures in 2019 was ongoing at the time of the Doha World Championships and she was not provisionally suspended at that time.
“Following conclusion of the investigation and a fourth whereabouts failure in January 2020, a notice of charge was issued and Ms Naser subject to an immediate provisional suspension.
“The disciplinary process is ongoing.”
Speaking on Saturday, Naser said: “I’ve never been a cheat. I will never be. I only missed three drug tests, which is normal. It happens.”
Explaining that the missed tests occurred before September’s World Championships, she added: “Hopefully, it’ll get resolved because I don’t really like the image. It’s going to be fine. It’s very hard to have this little stain on my name.”
World Athletics’ anti-doping rules say a whereabouts violation consists of any combination of three missed tests or filing failures in a 12-month period.
Naser, who was born in Nigeria but switched allegiance to Bahrain in 2014, is the first Asian woman to be world champion in the discipline.