Jamaican sprinter Steve Mullings has reportedly tested positive for a banned substance.
The 28-year-old is said to have used a masking agent which is usually employed to hide the use of banned subtances in the blood stream.
The allegation comes just 16 days before the start of the world championships in Daegu, South Korea.
The positive sample was allegedly taken at the Jamaican national trials in June.
There has so far been no comment from the Jamaica Anti-Doping Commission (JADCO) and the Jamaica Athletics Administrative Association (JAAA).