Italy's defending Olympic 50km race walk champion Alex Schwazer, who beat Australia's Jared Tallent in Beijing, has been caught doping and will miss the London Games.
The Italian Olympic Committee says Schwazer has tested positive for doping and has been removed from the team.
Earlier Monday, the team said an unidentified athlete had failed a doping test before arriving in London.
The 28-year-old Schwazer was due to defend his 2008 Olympic title in the 50km walk on Sunday against Tallent who won the silver medal at Beijing.
It is believed Schwazer tested positive for the banned blood booster EPO during a test conducted by the World Anti-Doping Agency at a training camp in Oberstdorf, Germany.
Schwazer admitted doping and said his career was over.
"My career is over. I made a mistake. I wanted to be stronger for this Olympics, I was wrong," Schwazer told Italy's ANSA news agency.
"I take full responsibility for what has happened. I did it by myself, it was my idea.
Schwazer was a bronze medallist at the 2005 and 2007 World Championships before winning gold at Beijing.