Australian equestrian rider Jamie Kermond has tested positive for cocaine and been suspended from the Tokyo Olympics.
The showjumper tested positive for a metabolite of cocaine on June 26, Equestrian Australia says.
Kermond's positive A sample came from a test conducted by Sport Integrity Australia [SPI].
Cocaine is prohibited under Australian and world anti-doping laws.
"Kermond is prohibited from participating in any WADA compliant event, including the Tokyo 2020 Olympic Games, while the provisional suspension is in place," an Equestrian Australia (EA) statement on Wednesday read.
Kermond acknowledged the positive test in a statement on Wednesday afternoon, attributing the result to a recent social event.
"Sport Integrity Australia informed me last night that I had tested positive to cocaine following a test last month," Kermond said.
"It is likely that positive result was from a single recreational use of the drug during a social event and had no connection with my sport of equestrian.
"The consequence of this positive result is that I have been provisionally suspended from my sport by Equestrian Australia."
Kermond said he would fully comply with the SPI investigation and would look to make amends for his actions in the future.
"I am extremely upset and remorseful as to what has happened, and I accept full responsibility. I am truly sorry as I have let a lot of people down including my family and teammates.
"Hopefully one day I can be forgiven for my mistake and make amends through better actions and continued contribution to the sport I know and love."
The 36-year-old from Victoria was to have been making his Olympic debut in Tokyo.
Kermond was selected as one of three showjumpers on a nine-strong Australian equestrian team at the Games.
"Equestrian Australia has spoken with Mr Kermond and support services will be offered to him," EA said.
His suspension is a blow to the Australian Olympic Committee (AOC) just two days out from the opening ceremony.
The AOC was told of Kermond's suspension by SPI, a newly-named body which has taken over anti-doping from ASADA.
"The Australian Olympic team selection committee will consider the matter later today," an AOC statement read earlier Wednesday.
Kermond is a triple Australian showjumping champion but his initial selection for the Olympics attracted scrutiny.
He's ranked 1013th on world standings but has links to one of two national selectors, Stephen Lamb.
Lamb is employed as marketing manager at a horse nutrition company which sponsor's Kermond's Yandoo Park, which offers agistment and training.
Selectors overlooked Rowan Willis, Australia's top-ranked rider at 59 in the world, and Lamb has said he stepped aside when Kermond's selection was discussed.
Equestrian Australia (EA) in June last year entered voluntary administration, with control of the elite program handed to the Australian Institute of Sport (AIS).
In May this year, EA wrote to the AIS to confirm proper governance practices were being followed in selecting the equestrian team for Tokyo, according to News Corp reports.