The 31-year-old has now been suspended by his team, Liberty Seguros, and will be sacked should a second, definitive, test on 21 November confirm the first finding.
The rider has insisted he is completely innocent, and that "my lawyers are on the case". Heras, whose possible positive occurred on the penultimate stage of the 2005 Tour of Spain, is a former team-mate of seven-times Tour de France winner Lance Armstrong.
Considered one of the sport's top climbers, on that stage, Heras came within a few fractions of a second of winning a time trial as well. Spain's most emblematic rider faces a two-year sanction if the test is confirmed.Reuse content