The American admitted to using performance-enhancing drugs during all seven of his victories at the Tour de France in an interview with Oprah Winfrey.
It came after cycling authorities stripped him of the titles when he refused to carry on his fight through the legal system.
"What a sad story," said the 17-time Grand Slam champion. "I don't know what to say. It just really saddens me to see that someone did this for such a long time.
"Obviously he's hurt his sport in a big way, even though he helped it in the beginning. But now the burden they live under, all other sports maybe as well.
"I'm an active athlete right now and it's not fun times really to be in sports to a degree."
When asked if he watched Armstrong's interview, he replied: "All I needed to see was the first few minutes of the interview and then I knew what was the deal and the rest I don't really care."
The Swiss will play Milos Roanic in the last 16 in Melbourne.