Russian walker Sergey Kirdyapkin could be stripped of his London 2012 gold following a successful IAAF appeal.
The men’s 50km walk gold medallist is one of six Russian athletes to have their results annulled.
The Court of Arbitration for Sport (Cas) ruled that Russia’s anti-doping agency (Rusada) had been “selective” in its disqualification periods.
Australian Jared Tallent is now set to be awarded the gold and Irishman Robert Heffernan the bronze.
All six Russian athletes are already serving doping bans.
Tallent, who finished second behind Kirdyapkin, tweeted: “History has been re-written… I am Olympic champion.”
A re-allocation of that result would also mean a bronze medal for Irish walker Heffernan.
The 38-year-old said: “I had to read it a few times just in case I made a mistake.
“That makes me an Olympic bronze medallist and it’s unreal.”
However, in its statement, Cas said it was “unable to comment on the corrections in the various rankings which may be affected by the present decision and the possible re-allocation of medals, titles, awards or prizes, as this is a matter for IAAF to determine”.
The other London 2012 result affected is the women’s 20km race walk, with Cas ruling that silver medallist Olga Kaniskina’s results should now be disqualified from August 2009 to October 2012.
And 3,000m steeplechase 2011 World Champion Yuliya Zaripova is now likely to lose her gold medal.
Other Russian athletes affected by the ruling are Olympic 2008 men’s 20km race walk winner Valery Borchin – currently serving an eight-year ban – plus 50km men’s race walk 2011 World Champion Sergey Bakulin and Vladimir Kanaikin, runner-up in the 2011 World Championship 20km men’s race walk.