Lance Armstrong, preparing for his final Tour de France in July, worries constantly about someone spiking his food with a performance-enhancing drug.
The record six times Tour champion also said in a wide-ranging interview with Playboy that he believes the image of his scandal-scarred sport is unfair.
"I like to think the sport is cleaner than its reputation," Armstrong said in the magazine's June edition.
"It's ironic that cycling has done more than any other endurance sport to test them, and when you test you're going to catch some guys."
Armstrong said every time a cyclist is caught using a banned substance someone "is sure to write, 'Look how dirty the sport is!' That's the risk of testing".
The American, who has survived cancer, estimates he has been tested for banned substances about 300 times in his career.
Asked how many times he had tested positive he replied: "Zero".
The 33-year-old always worries, though, that someone will slip a banned substance into his food or water.
"I worry about that every day," he said. "They could spike your food or the water you drink."
ATHLETES RESPONSIBLE
Armstrong said eventually professional franchises and sponsors "are going to hold the athletes responsible".
"If they're not clean, sponsors and teams will go after their money -- not just to stop paying salaries but to get back previous payments," he said.
"And that's serious because we all spend our money when we get it.
"If you're a baseball player who tests positive and your team wants your salary back from last year, can you get it back and repay them?"
Armstrong revels in uphill finishes and time trials and there will be fewer of both during this year's Tour, which will run from July 2-24.
"The three uphill finishes we'll have are super demanding," he said. "The final time trial is really hard. So there's no excuse for not winning.
"I can't roll into Paris and say the course was too easy," he added. "I'll have my opportunities to kick ass."
Armstrong said two things scare him.
"The first is getting hurt. But that's not nearly as scary as the second, which is losing.
"If you're caught behind a crash in a windy section with 50 guys in a pile in front of you -- game over."