World 400m champion Salwa Eid Naser has been given a provisional suspension for failing to make herself available for anti-doping tests.
The Bahraini, 22, ran 48.14 seconds – the third-fastest time in history – to claim the world title in Doha in 2019.
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.
She could face a ban of up to two years for the whereabouts violation.
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.