Former world champion Parker tested positive during a drugs test administered the same day he fought in 11th-round defeat to British heavyweight Ipswich-born Wardley.
The British boxer and Parker participated in a thrilling contest staged in the UK capital last October to decide the next mandatory WBO contender to unified heavyweight titleholder Ukrainian champion Usyk.
Parker had been the leading contender to challenge the champion subsequent to stringing together a remarkable six-fight winning streak, yet put his shot at the title at stake during the bout and experienced an 11th-round defeat.
A routine test administered to Parker through Vada the day of the match returned positive and now leaves Parker in a difficult position to clear his name.
His promotion team released a statement stating: "Vada informed everyone involved about Parker had a positive result after an anti-doping test conducted on the 25th October. During the ongoing inquiry, no further statements are planned at this time."
Parker was crowned world champion in 2016 before he lost his WBO belt via unanimous decision to British star Joshua at the Millennium Stadium in 2018.
The fighter became a frequent visitor on British soil since then, fighting eight times altogether in Britain and transferring to the Irish capital for preparation alongside respected coach Andy Lee over the past few years.
Coached by Andy Lee, Joseph Parker overcame his 2022 loss to Joe Joyce to achieve several successes positioning him as the top contender to face the champion before he was defeated to Wardley.
After Parker returned a failed test when he fought Wardley, reportedly involving cocaine, an investigation regarding the results is underway.
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