The New Zealand heavyweight produced a positive sample during a anti-doping examination carried out on the day of his 11th-round stoppage versus British heavyweight Fabio Wardley.
Wardley together with Parker were part of a thrilling bout in London last October to decide the next next in line for the WBO to undisputed world heavyweight champion Oleksandr Usyk.
The fighter was previously next in line to challenge the champion after compiling a remarkable six wins in a row, yet put his shot at the title in jeopardy in London and endured an 11th-round defeat.
A routine test administered to the boxer through Vada on the day of the bout came back positive and leaves Parker in a difficult position to demonstrate his cleanliness.
His promotion team published a statement declaring: "The agency alerted everyone involved regarding Joseph Parker tested positive after a drug screening conducted on the 25th October. During the ongoing inquiry, no more comments are planned currently."
Joseph Parker earned the title of heavyweight champion six years ago until he was defeated for his championship belt via unanimous decision against Anthony Joshua in Cardiff two years later.
The fighter has been a frequent visitor across the United Kingdom after that, fighting eight times in total in the UK and transferring to Dublin for training camps under respected coach Andy Lee over the past few years.
Guided by Lee, Joseph Parker overcame his 2022 loss versus British heavyweight Joyce to secure several successes which put him front of the queue to meet Oleksandr Usyk until he suffered defeat to the British fighter.
Following Parker's sample showed an adverse finding on the day of the Wardley fight, reportedly involving cocaine, a probe regarding the results has commenced.
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