Landis, who was stripped of his 2006 Tour title because of doping, told German television on Monday that he knows riders take clenbuterol.
"I think that the risk of taking clenbuterol is higher now than it was earlier, when there weren't any training controls," Landis said. "There is still the risk of being caught even if it is rather small now, since the product has usually degraded when the control takes place.
"You don't know what risks people will take to win a race."
Contador, who won his third Tour title earlier this year, . He is facing a two-year ban and could be stripped of his victory at an upcoming hearing before the Spanish cycling federation.
Landis has previously alleged that Lance Armstrong and members of their former U.S. Postal team systematically doped. A grand jury in Los Angeles has been hearing evidence from an investigation for months in closed sessions.
Landis said Monday that cycling's governing body "protects some people and not others."
"That is the way they manipulate results and create stars," said Landis, who acknowledged his own doping history when he rode for U.S. Postal and Phonak. "It is easy to take anabolics, whether it is testosterone, growth hormone or something like that; and EPO and to make blood transfusions. You can easily do all of that without getting caught, and we routinely did it."
Armstrong, a seven-time Tour winner, has always denied doping.