The Russian anti-doping agency says former world boxing champion Evgeny Gradovich has been banned for two years for breaking anti-doping rules.
The agency did not elaborate.
Gradovich's ban is backdated to June 30, 2015, a month after he lost his IBF featherweight title to Britain's Lee Selby, who still holds the belt.
The Russian has fought three times since that date, most recently on April 9, when he lost to Mexican fighter Oscar Valdez in Las Vegas for the WBO's North American featherweight title.
The WBO did not immediately respond to a request for comment from The Associated Press.
This month, another Russian fighter, Igor Mikhalkin was stripped of his European light heavyweight title after a positive test for the banned substance meldonium.