The New Zealand heavyweight produced a positive sample in a anti-doping examination conducted the very day he faced 11th-round stoppage versus English fighter Fabio Wardley.
The British boxer and Parker engaged in a pulsating bout held in London on 25 October to determine the next WBO mandatory challenger to unified heavyweight titleholder Oleksandr Usyk.
The fighter was previously the leading contender to meet the champion after compiling an impressive six consecutive victories, however placed his mandatory challenger status on the line during the bout and endured an 11th-round stoppage.
A routine test conducted on Parker via the Voluntary Anti-Doping Agency the day of the match came back positive which leaves Parker with a battle to demonstrate his cleanliness.
His promotion team issued a statement which read: "The anti-doping body notified all required parties regarding Joseph Parker returned an adverse finding after a drug screening carried out on October 25th. As the investigation continues, no additional comment will be made currently."
The New Zealand boxer earned the title of heavyweight champion back in 2016 until he lost the WBO title through a points decision versus Anthony Joshua in Cardiff 24 months later.
Joseph Parker remained an active participant in the UK since then, fighting eight times in total in Britain and moving to the Irish capital for fight camps under highly regarded trainer Andy Lee during this period.
Under the tutelage of Lee, Parker overcame his 2022 loss against Joe Joyce to chalk up a string of victories positioning him at the front of the line to challenge Oleksandr Usyk until he was defeated to Wardley.
After Parker returned an adverse finding when he fought Wardley, allegedly for cocaine, a probe about the test outcome is underway.
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