Lucian Bute’s B sample tested positive for the banned substance ostarine on Friday, just as his A sample did in May, the DC Boxing Commission confirmed to RingTV.com.

Bute’s initial positive test for ostarine marred his majority draw against super middleweight titleholder Badou Jack on April 30 at the DC Armory in Washington, D.C. Ostarine can be used as an endurance enhancer and has been on the World Anti-Doping Agency list of banned substances since 2008. The DC Commission has not made a decision on punishment, but the bout’s result will likely be changed to a no-decision and Bute should face a suspension.

As the news of the B sample’s findings came to light, Bute, 36 and promoter Yvon Michel immediately set to defend themselves, alleging that Bute (32-3-1, 25 knockouts) didn’t knowingly take the substance and had consumed a contaminated supplement in the run-up to the bout.

According to a release put out by Michel, the boxer took a “supplement formula prescribed by physical trainer Angel Heredia” called Dynamita that “had been contaminated during preparation of this supplement at the Pharmagenic laboratory” for traces of ostarine. The promoter lay the blame at the foot of  Pharmagenic labs in San Diego, according to the release. Heredia did not immediately return a message for comment.

“Bute and his lawyer intend to pursue legal proceedings against the laboratory that has caused irreparable harm to the integrity and reputation of the former IBF super middleweight champion,” the release said. “Details of the investigation were forwarded to the athletic commission in Washington DC, which will therefore be inviting Bute to enable representations and explanations of what happened before it takes a decision.”