Lance Armstrong is not losing any sleep over a U.S. federal investigation into allegations of doping in his team, the seven-times Tour de France champion said on Saturday ahead of his final international race.

The American will end an illustrious international career when he rides for his Team RadioShack at the Tour Down Under starting on Sunday.

Former team mate and disgraced 2006 champion Floyd Landis had alleged that Armstrong and several others had used performance-enhancing drugs, triggering a U.S. federal investigation.

I never lose sleep... ever, the 39-year old said. It has no effect on my life -- zero. That's for other people to deal with.

I have five kids to raise, a foundation (for cancer research) to run, I still have, theoretically, a job and I don't let it affect me, he added. I try to keep my head held high.

Armstrong, who has never tested positive, denied any wrongdoing and said it would have been impossible to get away with doping over a decade.

They can keep looking, he said. If you're trying to hide something, you wouldn't keep getting away with it for 10 years, nobody is that clever.

Cancer survivor Armstrong also admitted his return to cycling, which started two years ago in Adelaide, could not be considered a success, at least from a sporting perspective.

I really thought I'd win an eighth Tour de France and I was outclassed by better riders, he said.

I found myself against younger and stronger guys but I have absolutely no regrets because from the foundation's perspective, it has certainly been a success.