Showjumper Jamie Kermond was kicked off the Australian Olympic team Wednesday after testing positive for cocaine, with the remorseful rider saying the result was likely from taking the drug at a social event.
The 36-year-old returned a positive A-sample on June 26 following a test by Sport Integrity Australia, with the result only made public Wednesday.
"It is likely that the positive result was from a single recreational use of the drug at a social event and had no connection with my sport of equestrian," the 36-year-old said in a statement.
"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."
According to Australian reports, Kermond did not travel with the rest of the team when they flew to Tokyo on Tuesday.
Equestrian Australia said Kermond had been provisionally suspended from all competition, including the Olympics, and the Australian Olympic Committee later issued a statement confirming he would take no part in Tokyo.
"The Australian Olympic Team chef de mission Ian Chesterman has announced that the Australian Olympic Team selection committee met and has terminated equestrian athlete Jamie Kermond's membership of the Tokyo 2020 Australian Olympic team," the AOC said.
It pointed to Kermond breaching several clauses in the team agreement by bringing the sport into disrepute and not taking all possible measures to ensure he was in top physical and mental condition.
Under Australia's anti-doping policy, he has the opportunity to have his B-sample analysed.
Kermond was due to be part of a nine-strong Australian equestrian team headlined by eventing star Andrew Hoy, a three-time gold medallist who is at his eighth Olympics, and dressage veteran Mary Hanna at her sixth Games.
He was set to make his Olympic debut on his horse Yandoo Oaks Constellation, but was not seen as a serious gold medal contender.