Joseph Parker is back at his Las Vegas base preparing for the second defence of his WBO belt in September.

Joseph Parker's missed drug test was a result of the Kiwi world boxing champion not notifying authorities of his extended holiday, his promoters have said.

One of four major sanctioning bodies in the sport, on Monday (Tuesday NZ time) the World Boxing Council (WBC) listed Parker as one of five to miss a test during the first part of 2017 as part of their Clean Boxing Program administered by the Voluntary Anti-Doping Association (Vada).

A spokesman for Duco Events, Parker's promoters, confirmed to Stuff their fighter had missed a test after the successful first defence of his WBO heavyweight belt against Razvan Cojanu but said it was an oversight.

"Joseph extended his holiday following the Cojanu bout on May 6 and didn't update the Vada system of his change of plans.

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"A couple of weeks ago drug testers went to his residence in Las Vegas (Parker's training base) and he had said he was going to be in camp there but he had changed his plans and was in Samoa at the time.

"There is no hiding it's an oversight."

Vada's policy on their official website states any athlete who misses two or more tests during their period of registration with the organisation will be removed from the programme "at Vada's discretion".

Asked if Parker may be liable to any sort of punishment, Duco reiterated the indiscretion had been a simple oversight.

"A missed test doesn't mean you've been doping, it just means you've been careless.

"In this case it's just that Joseph didn't update the Vada system and he was on holiday at the time. There is no hiding the fact he missed a drug test and he has to take it on the chin.

"Joseph is back in camp in Vegas for the next eight weeks and Vada can stop by at any time of the day or night if they want to see him."

Vada testing involves informing the organisation where you going to be for one hour per day every day of the year.

Their Clean Boxing Program tested 72 fighters during "the first semester of 2017", with some tested multiple times, with 64 returning clean results and four (Andrej Wawrzyk, Cletus Seldin, Dennys Ceylan and Suriyan Khaikanha) returned adverse findings.

The five listed as missing tests were Parker, top-ranked heavyweight Bermane Stiverne, J'Leon Love, Kyotara Fujimoto and Tevin Farmer.

"Each missed test and adverse finding has been or is in the process of results management protocol," the WBC said in the release.

The WBC announced their Clean Boxing Program in May last year, saying it was professional boxing's "first year-round unannounced and random performance enhancing drug program".

As the WBO champion, Parker is no longer ranked in the top 15 of any of the other three major sanctioning bodies, the WBC, WBA and IBF.

With an unbeaten 23-0 record, he has just one fight on his resume with respected boxing website BoxRec where a WBC title was up for grabs.

Parker won the vacant WBC Eurasia Pacific Boxing Council heavyweight title in his 16th pro fight against Kali Meehan in October, 2015.

The belt, again vacant, was claimed by Russian fighter Sergey Kuzmin in April last year.