The international sports tribunal has stripped Russian runner Maria Savinova-Farnosova of the London Olympics 800-meters gold medal and banned her for four years for doping.
Savinova-Farnosova, 31, won the 800-meter title ahead of South Africa's Caster Semenya.
If the International Olympic Committee decides to reallocate the medals from the 2012 final, Semenya will add that gold medal to the one she won at the 2016 Summer Games in Rio de Janeiro.
The Lausanne-based Court of Arbitration for Sport (CAS) said there was "clear evidence" that Savinova-Farnosova was involved in doping from 2010 until 2013 -- including for the 2012 London Games.
The CAS acted as the main tribunal in the case, as the Russian track-and-field federation is suspended by the world body, the International Association of Athletics Federations because of its doping controversy.
In 2014, Savinova-Farnosova was filmed undercover by Russian doping whistle-blower Yulia Stepanova, and appeared to admit to injecting banned substances.
The footage helped spark a World Anti-Doping Agency (WADA) investigation into Russia, and led to Savinova-Farnosova's blood samples being reexamined.
Following further evidence of widespread drug use, the Russian track team was suspended from all international competitions in November 2015 and missed last year's Olympics.