Former world champion Parker tested positive in a drugs test administered the same day he faced 11th-round stoppage versus English fighter Fabio Wardley.
Fabio Wardley together with Joseph Parker participated in a pulsating encounter in London on 25 October to determine the identity of the next in line for the WBO facing undisputed world heavyweight champion Oleksandr Usyk.
Parker had been the leading contender to meet Usyk following stringing together a notable six wins in a row, but placed his shot at the title at stake in London and suffered a stoppage in round eleven.
An ordinary examination administered to the boxer via Vada on the day of the bout came back positive which leaves Parker with a battle to demonstrate his cleanliness.
Parker's promotional company published a communique stating: "The agency informed all relevant parties regarding Joseph Parker returned an adverse finding following a drug screening conducted on the 25th October. During the ongoing inquiry, no further statements are forthcoming at this time."
Joseph Parker became titleholder six years ago until he was defeated for his WBO belt by unanimous decision versus British star Joshua in Cardiff two years later.
Joseph Parker has been a frequent visitor in the UK since then, competing in eight bouts overall in the UK and transferring to Ireland for preparation with esteemed mentor former champion Lee over the past few years.
Guided by Lee, Joseph Parker overcame the 2022 setback against Joe Joyce to chalk up a string of victories positioning him as the top contender to meet Usyk before he was defeated against Wardley.
After Parker's sample showed an adverse finding when he fought Wardley, reportedly for cocaine, an inquiry about the test outcome has commenced.
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