Former world champion Parker produced a positive sample as part of a doping test carried out the same day he fought in 11th-round loss versus British heavyweight Fabio Wardley.
Fabio Wardley together with Parker participated in an intense bout held in London in late October to decide who would become next in line for the WBO against unified heavyweight titleholder Ukrainian champion Usyk.
Joseph Parker had positioned himself as the leading contender to challenge Usyk following putting together an impressive six wins in a row, but placed his mandatory challenger status in jeopardy during the bout and endured an 11th-round stoppage.
An ordinary examination given to Joseph Parker by the Voluntary Anti-Doping Agency the day of the match came back positive which leaves the veteran boxer in a difficult position to clear his name.
Parker's promotional company issued a statement which read: "The agency alerted all required parties about Parker tested positive after an anti-doping test administered on October 25th. As the investigation continues, no more comments are planned for now."
Joseph Parker was crowned world champion back in 2016 before he surrendered the WBO title by unanimous decision versus Anthony Joshua in Cardiff 24 months later.
Parker has been an active participant on British soil after that, having eight matches overall in the UK and transferring to Ireland for fight camps under highly regarded trainer Andy Lee in recent years.
Under the tutelage of Lee, Parker overcame his defeat in 2022 to Joe Joyce to secure multiple wins which put him as the top contender to challenge Oleksandr Usyk until he suffered defeat to the British fighter.
Following Parker's sample showed a failed test when he fought Wardley, reportedly for cocaine, an inquiry into the findings has commenced.
