The reigning Olympic champion in the 50km walk, Alex Schwazer, will not defend his title after a positive drugs test.
The Italian Athletics Federation (FIDAL) announced on Monday that Schwazer had been pulled out of their Olympics squad.
"This afternoon, FIDAL has received confirmation of the positive doping test of Alex Schwazer and the subsequent decision taken by CONI (the Italian Olympic Committee) to exclude him from their Olympic team," read a statement on the FIDAL website.
Schwazer was also entered in the men's 20km walk which took place on Saturday but withdrew last month, citing a cold.
At the time the 27-year-old made it clear he intended to defend his 50km title. He won silver at the shorter distance in Beijing.
He told Italian press agency ANSA: "I made a mistake, my career is ended here.
"I did it all myself and on my own head so I assume all the responsibility for what has happened.''
FIDAL president Franco Arese said: "Better that it happened before the race.
"If it had happened afterwards it would have been worse. We agree with CONI's decision to exclude him immediately from the Olympic team.
"He will be severely punished, as must be obvious, but I see from what he has said that he has had the courage to take full responsibility.
"I can't understand what made him do it. I am sure he did not need to. One day I will ask him.''
