Former world champion Parker returned an adverse finding as part of a drugs test administered the same day of his 11th-round stoppage versus British heavyweight Ipswich-born Wardley.
Wardley and Parker participated in an intense contest in London on 25 October to establish who would become mandatory WBO contender to undisputed world heavyweight champion Ukrainian champion Usyk.
The fighter was previously the leading contender to face Usyk following compiling a notable six consecutive victories, but risked his contender position in jeopardy in the UK and endured an 11th-round stoppage.
An ordinary examination administered to Joseph Parker via the anti-doping organization the day of the match showed an adverse result which leaves the veteran boxer in a difficult position to clear his name.
His promotion team published a statement declaring: "The anti-doping body notified all relevant parties that Joseph Parker had a positive result subsequent to a doping test conducted on October 25th. As the investigation continues, no additional comment will be made for now."
Parker was crowned world champion back in 2016 until he was defeated for his championship belt via unanimous decision against Anthony Joshua in Wales 24 months later.
Joseph Parker remained a frequent visitor on British soil after that, having eight matches in total in Britain and transferring to the Irish capital for preparation alongside esteemed mentor Andy Lee over the past few years.
Coached by Andy Lee, the boxer bounced back from his defeat in 2022 to Joe Joyce to achieve a string of victories that placed him front of the queue to meet Oleksandr Usyk prior to he was defeated against Wardley.
Following Parker returned a failed test when he fought Wardley, reportedly for cocaine, an investigation about the test outcome is underway.
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