The New Zealand heavyweight produced a positive sample as part of a anti-doping examination conducted the very day he fought in 11th-round stoppage to UK boxer Fabio Wardley.
The British boxer along with Parker engaged in an intense encounter held in London on 25 October to determine the next next in line for the WBO to reigning heavyweight king Oleksandr Usyk.
Parker had been the leading contender to challenge Oleksandr Usyk following putting together a remarkable six-fight winning streak, but put his mandatory challenger status at stake in the UK and experienced a stoppage in round eleven.
A routine test administered to Joseph Parker via the Voluntary Anti-Doping Agency the day he fought showed an adverse result which leaves the veteran boxer with a battle to prove his innocence.
His promotion team released a statement stating: "The anti-doping body notified all required parties about Parker returned an adverse finding following an anti-doping test conducted on the 25th October. While the matter is investigated, no additional comment will be made currently."
Parker was crowned world champion in 2016 prior to he surrendered his WBO belt through a points decision against British star Joshua at the Millennium Stadium two years later.
The fighter has been a regular competitor across the United Kingdom from that point, competing in eight bouts overall in Britain and relocating to Ireland for preparation alongside highly regarded trainer former champion Lee in recent years.
Guided by Lee, Parker recovered from the 2022 setback against Joe Joyce to secure a string of victories which put him at the front of the line to meet Usyk prior to he was defeated against Wardley.
Following Parker's sample showed a positive test on the day of the Wardley fight, allegedly for cocaine, a probe regarding the results has commenced.
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