Former world champion Parker returned an adverse finding as part of a doping test conducted the very day he faced 11th-round loss to UK boxer Fabio Wardley.
The British boxer along with the New Zealander engaged in an intense encounter in London last October to decide the identity of the mandatory WBO contender to reigning heavyweight king Oleksandr Usyk.
The fighter had positioned himself as the primary candidate to meet Oleksandr Usyk after stringing together a remarkable six wins in a row, yet placed his mandatory challenger status in jeopardy in the UK and suffered an 11th-round defeat.
A routine test administered to Parker via the Voluntary Anti-Doping Agency on the day of the bout came back positive and now leaves Parker with a battle to demonstrate his cleanliness.
The boxer's representatives issued an announcement declaring: "Vada notified all required parties about Parker returned an adverse finding after an anti-doping test conducted on October 25th. While the matter is investigated, no additional comment will be made for now."
Parker became world champion in 2016 before he was defeated for his WBO belt via unanimous decision to Anthony Joshua at the Millennium Stadium 24 months later.
The fighter has been an active participant in the UK since then, competing in eight bouts altogether in the UK and moving to Ireland for fight camps under respected coach Andy Lee during this period.
Under the tutelage of Lee, Joseph Parker recovered from his 2022 loss to Joe Joyce to chalk up several successes positioning him as the top contender to face the champion until he suffered defeat against Wardley.
Following the boxer produced a positive test during the Wardley bout, allegedly for cocaine, an investigation about the test outcome has been started.
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