Oscar Valdez remains hard at work for his next ring appearance, as his legal team has taken the lead on perhaps the most important fight of his career.

The unbeaten two-time and reigning WBC junior lightweight titlist is due to make his first defense versus Brazil’s Robson Conceicao (16-0, 8KOs), scheduled to take place September 10 live on ESPN+ from AVA Amphitheatre at Casino del Sol in Tucson, Arizona. There are now concerns regarding the event moving forward, in light of Valdez (29-0, 23KOs) producing a positive “A” sample for a banned substance as identified through random drug testing conducted by Voluntary Anti-Doping Association (VADA), as first noted through social media by ESPN.com boxing insider Mike Coppinger.

BoxingScene.com has learned that the substance in question is Phentermine, a dietary anorectic normally used as an appetite suppressor. The substance—a commonly prescribed weight-loss medication—is prohibited while in-competition under universally-recognized drug testing standards as classified by the World Anti-Doping Agency (WADA). 

According to information obtained by BoxingScene.com, the detected amount was a low concentration, though still enough to be flagged by VADA’s zero-tolerance policy.

“Based upon my experience and after discussion with Mr. Valdez I have a fair idea where the substance came from - more than possibly from an otherwise innocuous herbal tea,” Patrick English, Valdez’s attorney —regarding this matter—explained in a thirteen-page letter submitted to the WBC, VADA, Top Rank (Valdez’s promoter) and the Pascua Yaqui Tribe of Arizona, a copy of which has been obtained by BoxingScene.com. “However, there is an important threshold matter for me to bring to your attention. Phentermine is not a banned substance at this point in Mr. Valdez's training.”

The basis for English’s legal argument stems from substances classified as banned in-competition and out-of-competition through WADA code. However, VADA has its own list of banned substances, on which Phentermine is listed and identified as a prohibited stimulant.

VADA does not differentiate between in or out of competition. All substances on its current prohibited list are banned at all times, as specified on its website.

That said, VADA also does not have the authority to suspend athletes from competition, but rather report its findings to the presiding commission, the participants, and their respective teams. In this case, it would be up to the Pascua Yaqui Tribe of Arizona who is the presiding authority over the September 10 event. Commission members declined comment on the matter and neglected to discuss the process involved to clear a fighter’s name in such instances.

Representatives from VADA did not respond to a request seeking comment. Neither Top Rank nor members of the respective teams for Valdez or Conceicao were in a position to comment as the matter is currently under investigation.

The event is still scheduled to move forward, though the status is understandably in jeopardy given current developments. As is the case with all drug testing matters, Valdez has the right to call for his “B” Sample to be tested. Alternatively, his team can move forward with a hearing at which time they will have the opportunity to prove contamination or any means other than intention by which the product in question was ingested.

It will not necessarily clear him with VADA, whose rules are specific in citing the athlete as being responsible for what enters their system. The drug testing organization also discourages the use of supplements of any kind, as noted on all paperwork which participants are required to fill out upon enrollment into the program.

“We note that Mr. Valdez had no knowledge that he was taking Phentermine and that we believe at this point it come from an herbal tea,” English theorizes. “This shows the tremendous value of VADA testing. Had this not shown up it is very possible that an "in competition" test would have caught Phentermine with dire consequences. He is now alerted to the issue and has ceased taking anything possibly contaminated.”

Valdez remains in the gym in preparation of the upcoming title defense, which takes place in his childhood hometown. The two-time Olympian for Mexico and two-division titlist posted on his Instagram Live training videos from earlier Tuesday at trainer Eddy Reynoso’s facility in San Diego.

Valdez won the WBC junior lightweight title via tenth-round knockout of long-reigning champion Miguel Berchelt this past February 20 at MGM Grand Conference Center in Las Vegas. Both boxers were enrolled in VADÅ random drug testing for the fight.

The win came nearly two years after Valdez’s previous title fight, a twelve-round decision win over Jason Sanchez in the final defense of the WBO featherweight belt he held dating back to a July 2016 knockout win over then-unbeaten Matias Rueda in their vacant title fight.

Conceicao enters his first career title fight, assuming the fight moves forward as planned. The three-time Olympian who became Brazil’s first boxer to win Gold in 2016 Rio is coming off a seventh-round knockout of Jesus Antonio Ahumada this past April in Tulsa, Oklahoma. In his previous outing, the 32-year-old Brazilian survived a knockdown and two point deductions to edge Luis Coria in their ten-round thriller last October in Las Vegas.

Jake Donovan is a senior writer for BoxingScene.com. Twitter: @JakeNDaBox