Disgraced cyclist Floyd Landis has placed doubt on reigning Tour de France champion Alberto Contador’s claims that a positive test for clenbuterol was down to contaminated meat.

And the American, speaking on German television, claimed that world cycling chiefs have protected top riders from the scandal of positive doping tests for the past 20 years.

Contador, who has won the race’s yellow jersey three times, is facing an uncertain future. He is currently suspended provisionally as anti-doping experts decide whether a positive test for trace amounts of the banned weight loss/muscle building drug at the 2010 race merits a lengthy ban.

Landis knows a thing or two about doping practices. He was stripped of the 2006 Tour de France crown after a positive test for testosterone, and despite denying doping for four years he finally confessed several months ago.

In making his confession, he alleged that former team-mate Lance Armstrong was involved in systematic doping during his spectacular Tour de France career.

Those claims have since prompted a federal investigation into the American.

Landis said that despite even tighter controls by the sport’s governing body the UCI, clenbuterol is still used in the peloton.

“I know of riders taking clenbuterol. The chances of getting caught are higher than they used to be, but they’re still quite small because the drug usually disappears before the test,” said Landis.