The heavyweight championship fight between Deontay Wilder and Alexander Povetkin appears to be in serious jeopardy. Wilder was scheduled to put his WBC heavyweight title on the line on May 21 in Moscow, but the challenger failed a random drug test, ESPN's Dan Rafael first reported. The longtime boxing reporter posted on Twitter that Povetkin tested positive for meldonium in a urine test conducted by the Voluntary Anti-Doping Association (VADA), and it was later confirmed by VADA president.

"This letter is to advise you that the 'A' sample urine specimen number 3969608 collected from Alexander Povetkin on April 27, 2016 in Chekhov, Russia through his participation in the Voluntary Anti-Doping Association (VADA) program has been analyzed for anabolic agents, diuretics, beta-2 agonists, stimulants and drugs of abuse," VADA president Dr. Margaret Goodman wrote in a letter to both boxing camps. "The results of the analysis are as follows: Adverse. Urine specimen contains meldonium."

Meldonium was added to the World Anti-Doping Agency’s (WADA) list of banned substances on Jan. 1, 2016, and tennis star Maria Sharapova made headlines when she was found to have taken it early this year.

When an athlete submits urine for a drug test, his “A” sample is tested first. If that results in a positive test, his “B” sample is tested in order to rule out the possibility of a false positive. WBC president Mauricio Sulaiman won’t cancel the fight until the results of the “B” sample are revealed, but it’s certainly not looking good for Povetkin.

Wilder has been perfect to start his boxing career, going 36-0 with 35 knockouts. He’s arguably the best American heavyweight in the last decade, though he has yet to prove himself against a top opponent. A victory in Russia over Povetkin would have bolstered Wilder's reputation ahead of a potential unification bout with the winner of Tyson Fury and Wladimir Klitschko.

Povetkin has won his last four fights, suffering his only ever loss to Klitschko in 2013.