Former world champion Parker tested positive in a anti-doping examination administered on the day of his 11th-round defeat to UK boxer Fabio Wardley.
The British boxer and Parker were part of a pulsating encounter in London on 25 October to decide the identity of the next in line for the WBO against unified heavyweight titleholder Oleksandr Usyk.
The fighter had been the primary candidate to challenge Oleksandr Usyk after putting together a notable six wins in a row, yet placed his contender position on the line in London and experienced an 11th-round stoppage.
An ordinary examination conducted on the boxer via Vada the day of the match showed an adverse result and now leaves Parker with a battle to clear his name.
Parker's promotional company issued a statement stating: "The anti-doping body alerted all required parties that Joseph Parker had a positive result following an anti-doping test conducted on the 25th October. During the ongoing inquiry, no additional comment are planned for now."
The New Zealand boxer was crowned heavyweight champion six years ago until he lost his WBO belt by unanimous decision against British star Joshua in Cardiff two years later.
Joseph Parker has been a frequent visitor across the United Kingdom from that point, competing in eight bouts overall in the UK and moving to Dublin for preparation with respected coach Andy Lee over the past few years.
Guided by Lee, Parker overcame his defeat in 2022 to Joe Joyce to achieve a string of victories that placed him at the front of the line to challenge Oleksandr Usyk prior to he suffered defeat to Wardley.
Subsequent to Parker returned a positive test during the Wardley bout, reportedly for cocaine, an investigation about the test outcome has commenced.
A seasoned gambling analyst with over a decade of experience in online casino reviews and player strategy development.