Five-time Olympic medalist Marion Jones is reported to have failed an initial drug test at the recent U.S. championships in Indianapolis.
Sources with knowledge of the results said Jones' first urine sample tested positive for a performance-enhancing substance commonly known as EPO, or erythropoietin, at the event in June, where she won the 100-meters championship.
If her second sample also tests positive, she faces a minimum two-year ban from the sport.
Jones has been dogged by allegations that she has taken performance-enhancing drugs since 2003, when she was linked to the BALCO steroids scandal.
Reports that she failed the drug test came hours after she pulled out of the Weltklasse Golden League athletics meet in Zurich for what has been described as "personal reasons." The meet director says Jones received a phone call from the United States Friday that prompted her withdrawal.
Jones has won twice on the Golden League circuit this year - in Paris and Lausanne. She was not invited to compete in the Golden League final in Berlin next month because of her connection with coach Trevor Graham.
Graham coaches world and Olympic champion Justin Gatlin of the United States, who is under investigation after testing positive for steroids in April. The U.S. Olympic Committee has barred Graham and his athletes from using its training facilities pending the outcome of the investigation.
Some information for this report provided by AP and Reuters.