Former world champion Parker produced a positive sample in a doping test carried out the same day he fought in 11th-round stoppage to English fighter Fabio Wardley.
Fabio Wardley along with Parker engaged in a thrilling contest staged in the UK capital last October to decide the next WBO mandatory challenger to unified heavyweight titleholder Ukrainian champion Usyk.
The fighter was previously next in line to face Usyk subsequent to stringing together a notable six wins in a row, but risked his mandatory challenger status at stake in London and suffered an 11th-round defeat.
An ordinary examination administered to Parker through Vada the day he fought came back positive which leaves the veteran boxer facing a challenge to prove his innocence.
Parker's promotional company released a communique which read: "Vada alerted all required parties regarding Joseph Parker returned an adverse finding subsequent to a drug screening conducted on the fight day. As the investigation continues, no more comments will be made at this time."
Parker became world champion in 2016 prior to he surrendered his championship belt via unanimous decision versus Anthony Joshua at the Millennium Stadium two years later.
The fighter became an active participant in the UK from that point, having eight matches in total in the UK and transferring to Dublin for preparation with esteemed mentor Andy Lee over the past few years.
Coached by Andy Lee, Joseph Parker recovered from his 2022 loss versus Joe Joyce to achieve multiple wins which put him at the front of the line to face Usyk before he was defeated to the British fighter.
After the boxer produced a failed test during the Wardley bout, reportedly for cocaine, an investigation about the test outcome has been started.
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