America's Shawn Crawford, the 2004 Olympic 200m gold medallist, has been banned for two years for not complying with out-of-competition drugs testing.
The US Anti-Doping Agency (Usada) said the 35-year-old failed to provide details of his whereabouts for testing on three occasions within 18 months.
He will be stripped of any result he achieved from 17 November, 2012, the date of his third failure to comply.
Crawford won silver in the 200m and the 4x100m relay at the Beijing Olympics.
In 2003, he took part in a US television programme that saw him race against a zebra and a giraffe. He beat the giraffe but lost twice to the zebra after demanding a rematch following a false start.
In 2004, Crawford won the Olympic 200m title, clocking a personal best of 19.79 seconds to defeat compatriots Bernard Williams and Justin Gatlin.
When Usain Bolt won the first of his Olympic 200m titles in Beijing in 2008, Crawford originally finished fourth, but was given the silver medal after Wallace Spearmon and Churandy Martina of Netherlands Antilles were disqualified for running out of their lanes.
Crawford later gave his medal to Martina, who would have been the first Olympic medallist from his country.
Crawford failed to qualify for London 2012 after finishing seventh in the US trials final.
Usada also confirmed that Crawford's ban would begin from 17 April, the date he received the sanction.
Shawn Crawford
Gold: 2004 Olympic 200m, 2001 World Indoor Championships 200m
Silver: 2008 Olympic 200m, 2004 Olympic 4x100m relay, 2004 World Indoor Championships 60m
Bronze: 2001 World Championships 200m