The New Zealand heavyweight tested positive in a drugs test carried out the same day he fought in 11th-round defeat to British heavyweight Ipswich-born Wardley.
The British boxer and Parker participated in an intense encounter staged in the UK capital last October to determine who would become mandatory WBO contender to unified heavyweight titleholder Ukrainian champion Usyk.
The fighter had been the leading contender to face Usyk after stringing together a notable six wins in a row, but risked his mandatory challenger status on the line in London and endured a stoppage in round eleven.
A standard screening conducted on Joseph Parker through the Voluntary Anti-Doping Agency the day of the match returned positive and leaves Parker with a battle to demonstrate his cleanliness.
His promotion team published an announcement stating: "The anti-doping body notified all required parties that Joseph Parker tested positive subsequent to a doping test conducted on the fight day. As the investigation continues, no further statements are forthcoming for now."
The New Zealand boxer became heavyweight champion six years ago before he was defeated for his WBO belt by unanimous decision against Anthony Joshua in Cardiff in 2018.
The fighter became a regular competitor in the UK from that point, competing in eight bouts altogether on UK territory and relocating to the Irish capital for training camps under esteemed mentor Andy Lee during this period.
Under the tutelage of Lee, the boxer overcame the 2022 setback versus Joe Joyce to secure multiple wins that placed him at the front of the line to face Usyk until he was defeated to Wardley.
Subsequent to Parker's sample showed a positive test during the Wardley bout, allegedly for cocaine, a probe about the test outcome has been started.
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Michelle Beard
Michelle Beard
Michelle Beard
Michelle Beard
Michelle Beard