Former world heavyweight boxing champion Joseph Parker on Saturday denied taking a prohibited substance after failing a doping test, expressing confidence an investigation would clear his name.

The 33-year-old New Zealander, whose whereabouts were unclear, failed the test on the day he fought and lost to Britain's Fabio Wardley last month, said his promoter, Frank Warren's Queensberry Promotions.

British media said he had tested positive for traces of cocaine and could face a lengthy ban from the sport.

"Before my recent fight I took a voluntary test and have now been informed that it returned an adverse result. This came as a real surprise to me," Parker said in a statement on Instagram.

"I did not take any prohibited substance, I do not use performance enhancing drugs and do not support their use. I am cooperating fully with the process now underway, and I am confident the investigation will clear my name.

"Thank you to everyone who has sent messages of support. It means a great deal to me and my family. When the investigation is complete, I will speak openly and answer questions."

Parker won the WBO heavyweight title in 2016 by defeating Mexican Andy Ruiz for the vacant belt. He lost the title to Britain's Anthony Joshua in 2018.

He had held the WBO interim heavyweight title since March last year after defeating China's Zhang Zhilei.