Joseph Parker produced a positive sample during a drugs test administered the same day he faced 11th-round loss to English fighter Fabio Wardley.
Fabio Wardley together with Parker engaged in an intense contest staged in the UK capital in late October to determine the next mandatory WBO contender to undisputed world heavyweight champion Oleksandr Usyk.
Parker had been the leading contender to face the champion after putting together an impressive six wins in a row, but risked his shot at the title on the line during the bout and suffered an 11th-round stoppage.
An ordinary examination given to Joseph Parker through Vada the day of the match came back positive and leaves the 36-year-old facing a challenge to clear his name.
The boxer's representatives published a statement stating: "The agency alerted all required parties regarding Joseph Parker tested positive following a doping test carried out on October 25th. As the investigation continues, no further statements will be made at this time."
The New Zealand boxer became world champion six years ago prior to he surrendered his championship belt by unanimous decision to Anthony Joshua in Wales two years later.
Parker remained a regular competitor on British soil since then, fighting eight times in total in Britain and relocating to the Irish capital for fight camps under respected coach Andy Lee over the past few years.
Guided by Lee, Parker recovered from his defeat in 2022 to Joe Joyce to chalk up a string of victories positioning him front of the queue to challenge Usyk before he suffered defeat to Wardley.
After Parker returned a positive test on the day of the Wardley fight, reportedly involving cocaine, an inquiry about the test outcome is underway.
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