Joseph Parker has reaffirmed his commitment to drug-free boxing, in the wake of Russian heavyweight Alexander Povetkin's positive drug test.

Povetkin, an Olympic gold medallist and former WBA world champion, was the only man to have knocked out Carlos Takam, who Parker is set to fight in Manukau this weekend.

Parker, who is busy preparing for the fight, where the winner will become the mandatory challenger to Britain's Anthony Joshua for the IBF title, said there was no place for drugs in their sport.

"Boxing has got to be drug free and that's the reason we do drug tests and we've just got to keep it clean," said Parker.

"We have a drug test this week before the fight and I look forward to that."

Povetkin was set to fight WBC heavyweight champion Deontay Wilder in Moscow on the same day as the Parker-Takam fight, but the WBC has now postponed it.

Parker's trainer, Kevin Barry, said the postponement of the Wilder fight would lead to extra attention being placed on his fighter.

"This is a fight, Povetkin and Wilder for the WBC title, which boxing fans and sporting fans around the world have been waiting for. They've been making this fight for a long time and now for it not to take place is a real disappointment.

"This is fantastic news for our promotion here in New Zealand because the eyes of the boxing world will be on Joseph Parker versus Carlos Takam. This fight will take even more interest in the boxing and sporting world."

The WBC says the May 21 fight between Wilder and Povetkin in Moscow is off, pending an investigation, with no backup date.

"Keeping the priority of safety and also the principle of justice, the WBC will continue the investigation into the case," the WBC said in a statement.

"Consequently, the event scheduled for May 21 in Moscow is hereby officially postponed."

It added that "the WBC will be releasing more information in the coming days regarding the final ruling on the matter".

Povetkin's promoter has said the substance found in an April test was meldonium, the stamina booster for which tennis star Maria Sharapova and dozens of other athletes in ex-Soviet nations have tested positive since it was banned at the start of this year.

Wilder had made allegations against Povetkin in an interview last year with USA Today. Wilder said he believed the Russian to be "on some kind of steroids" but said he was still willing to fight him.

Ryabinsky said that he accepted the WBC's ruling and hopes to restage the fight at a later date once the meldonium is out of Povetkin's system. "It'll happen but on another date," he said in a statement.

Athletes in several sports have avoided suspensions for meldonium positive tests under new World Anti-Doping Agency guidance issued in April - if the concentration of the heart drug is low enough to indicate they did not take it after January 1.

It is not clear whether such guidance will apply in the case of Povetkin. The WBC works with the Las Vegas-based Voluntary Anti-Doping Association, which often follows WADA's example but is not under its supervision.