Tour de France champion Alberto Contador has tested positive to a banned substance in news that will send shockwaves through the cycling world.

Cycling authorities have confirmed Contador did fail a test but say his reading for the banned stimulant is very small.

Alberto Contador of team Astana celebrates with his traditional pistol pose after winning this year's Tour de France. Credit:Getty Images

‘‘The concentration found by the laboratory was estimated at 50 picograms (or 0,000 000 000 05 grams per ml) which is 400 times less than what the antidoping laboratories accredited by WADA must be able to detect," said a statement from the Union Cyclist International (UCI).

‘‘In view of this very small concentration and in consultation with WADA, the UCI immediately had the proper results management proceedings conducted including the analysis of B sample that confirmed the first result.