The New Zealand heavyweight returned an adverse finding during a drugs test carried out on the day he faced 11th-round loss to English fighter Fabio Wardley.
Fabio Wardley together with Parker engaged in a thrilling bout held in London last October to decide who would become mandatory WBO contender against unified heavyweight titleholder Oleksandr Usyk.
Parker had positioned himself as the primary candidate to challenge Usyk after compiling a remarkable six consecutive victories, yet put his mandatory challenger status at stake in the UK and endured an 11th-round defeat.
An ordinary examination conducted on the boxer by the anti-doping organization on the day of the bout came back positive and now leaves the veteran boxer with a battle to clear his name.
Parker's promotional company released a communique which read: "The anti-doping body informed all relevant parties that Joseph Parker had a positive result after an anti-doping test carried out on the fight day. During the ongoing inquiry, no more comments will be made for now."
Parker earned the title of titleholder back in 2016 before he lost his championship belt by unanimous decision versus Anthony Joshua in Wales in 2018.
Parker has been a frequent visitor across the United Kingdom from that point, having eight matches overall in the UK and moving to Dublin for preparation under respected coach former champion Lee during this period.
Guided by Lee, the boxer overcame the 2022 setback to British heavyweight Joyce to achieve several successes positioning him front of the queue to face Usyk before he was defeated to the British fighter.
Following Parker's sample showed an adverse finding during the Wardley bout, reportedly involving cocaine, a probe about the test outcome has commenced.
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