Former world champion Parker returned an adverse finding in a anti-doping examination conducted on the day of his 11th-round loss against UK boxer Ipswich-born Wardley.
Fabio Wardley and Parker were part of an intense bout in London last October to determine who would become next in line for the WBO against unified heavyweight titleholder Oleksandr Usyk.
Joseph Parker had positioned himself as next in line to challenge Usyk after putting together a notable six consecutive victories, but put his mandatory challenger status on the line in London and endured an 11th-round stoppage.
A standard screening given to the boxer via the anti-doping organization the day he fought came back positive and leaves Parker in a difficult position to demonstrate his cleanliness.
The boxer's representatives issued an announcement which read: "The agency informed everyone involved regarding Joseph Parker had a positive result after a drug screening administered on the 25th October. During the ongoing inquiry, no more comments are forthcoming at this time."
Parker became titleholder in 2016 until he was defeated for his championship belt via unanimous decision to Anthony Joshua in Wales in 2018.
Parker became a regular competitor across the United Kingdom since then, fighting eight times in total in the UK and moving to Ireland for preparation alongside esteemed mentor former champion Lee over the past few years.
Coached by Andy Lee, Joseph Parker bounced back from his 2022 loss to Joe Joyce to achieve several successes that placed him front of the queue to meet Usyk before he lost to the British fighter.
Subsequent to Parker's sample showed a failed test on the day of the Wardley fight, reportedly involving cocaine, an inquiry into the findings has commenced.