Joseph Parker has missed a World Boxing Council jurisdiction drugs test.
The organisation listed Parker among five boxers as having "missed tests" in their "Midyear Clean Boxing Program Testing Report".
The Voluntary Anti-Doping Association (Vada) runs the WBC's testing programme.
They have conducted tests on 73 fighters in 2017, with 64 returning clean results and four - Andrej Wawrzyk, Cletus Seldin, Dennys Ceylan and Suriyan Khaikanha - delivering what were described as "adverse findings". Some boxers were tested multiple times.
In a statement, Parker's promoters Duco Events confirmed the news, but said their charge had been "careless", rather than "doping".
"Joseph extended his holiday following the [Razvan] Cojanu bout on May 6 and didn't update the Vada system of his change of plans.
"A couple of weeks ago, drug testers went to his residence in Las Vegas. He said he was going to be in camp there, but he had changed his plans and was in Samoa."
Parker, the WBO heavyweight champion, is set to defend his belt against unbeaten Englishman Hughie Fury in Manchester on September 23.
He was ringside at Fury's warm-up fight in London on July 8 with promoter David Higgins.
Duco said Parker had to "take it on the chin".
"There is no hiding, it's an oversight. A missed test doesn't mean you've been doping, it just means you've been careless.
"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's testing process involves athletes informing the organisation where they are going to be for one hour per day, from 6am-11pm, every day of the year. The procedure is similar to the "Whereabouts" programme, operated by the rival World Anti-Doping Agency, which oversees most international sporting codes.
Any athlete who misses two or more Vada tests during their period of registration with the organisation will be removed from the programme "at Vada's discretion".
Athletes must be at a precise location specified on the "Whereabouts Form" for the entire 60-minute period, and provide sufficient information to enable a tester to find and gain access to the location to find the athlete.
Essentially, all Parker had to do was send an email informing Vada of the changes.
Vada policy states: "Immediately upon learning that any information in a previously provided Vada Whereabouts Form is incomplete, inaccurate, or has changed in any manner, the athlete must communicate such changed information to Vada by completing and filing a new Whereabouts Form - either a hard copy or an electronic submission."
Vada claims a Wada-approved laboratory conducts the tests, and an internationally recognised anti-doping group collects the specimens and maintains the chain of custody.