Former world champion Joseph Parker has failed a drugs test, promoter Queensberry confirmed on Friday.
The New Zealander reportedly tested positive for cocaine the day of his controversial 11th-round defeat to Fabio Wardley, which took place on October 25 at London's O2 Arena.
According to widespread reports, traces of the drug were discovered in a routine test given to the Voluntary Anti-Doping Agency (VADA).
The 36-year-old now faces a battle to prove his innocence. If found guilty, Parker faces a lengthy doping ban.
Parker's promotional company Queensberry released a statement on Friday morning, which read: "The Voluntary Anti-Doping Association (VADA) last night informed all required parties that Joseph Parker returned an adverse finding following an anti-doping test conducted on the 25th October in relation to his bout with Fabio Wardley.
"While the matter is investigated further, no additional comment will be made at this time."
According to the National Drug and Alcohol Screening Association (NDASA), cocaine can be detected in urine up to four days after consumption.
Before losing to Wardley, New Zealander Parker was being lined up to face four-belt world heavyweight champion Oleksandr Usyk in 2026.
Parker was previously heavyweight champion between 2016 and 2018, before losing to Anthony Joshua.
Standard Sport have contacted VADA, British Boxing Board of Control (BBBofC) and UK Anti-Doping (UKAD) for comment.
