Australian Olympic middle-distance runner Peter Bol is pleading innocence after failing a test for a notorious performance-enhancing drug.
Bol, among the world's best 800m runners, has been provisionally suspended from athletics and could be stripped of a state Young Australian of the Year award.
Australia's national 800m record holder tested positive to the banned drug erythropoietin, known as EPO, last October.
The 28-year-old says he was stunned when told of the test result last week.
"I am innocent and have not taken this substance as I am accused," Bol posted on Twitter.
"I ask that everyone in Australia believe me."
Bol, arguably the nation's highest-profile track athlete, has been provisionally suspended by Athletics Australia.
The dual Olympian and Commonwealth Games silver medallist said his "career, hopes and dreams" hinge on the result of a B sample from the October test which would be known next month.
"When I found out last week that the A Sample from a urine test taken on 11 October had tested positive for synthetic EPO, I was in total shock," he wrote.
"To be clear, I have NEVER in my life purchased, researched, possessed, administered, or used synthetic EPO or any other prohibited substance.
"I voluntarily turned over my laptop, iPad and phone to Sport Integrity Australia to prove this.
"I have requested the analysis of my B Sample which will take place in February.
"Given the subjective nature of interpreting this kind of test, I have asked that the lab perform a secondary confirmation.
"Above all, I remain hopeful that the process will exonerate me.
"My career, hopes and dreams are literally hanging in the balance over these next few weeks."
The Sudanese-born runner could also be stripped of his West Australian Young Australian of the Year award. He was a candidate for the national award to be announced in Canberra next week.
Athletics Australia provisionally banned Bol from formal training and competition at any level, the organisation's chief executive Peter Bromley said.
"There are procedural fairness and investigative considerations ... at this point it would be inappropriate for Athletics Australia or anyone else to speculate about the specific details or pre-empt any outcome," Bromley said in a statement.
"However what we can say is that learning about this adverse analytical finding was both extremely concerning and completely out of the blue."
Bol, who emigrated to Australia with his family when eight years old, competed at the 2016 Rio Olympics and the Tokyo Olympics in 2021, when he placed fourth in the 800m final.
In Tokyo, Bol broke the national 800m record en route to being the first Australian in 52 years to reach the Olympic final in his pet event.
Bol lowered his national 800m benchmark at a Diamond League meet in Paris in June last year and then won Commonwealth Games silver over the distance in Birmingham in August.