"What a sad story," Federer said after his three-set win Saturday over Bernard Tomic at the Australian Open. "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."
Federer, a 17-time major winner, said he watched the first portion of the interview that Armstrong did with Oprah Winfrey.
"I guess all I needed to see was the first few minutes and then I knew what was the deal, and the rest I don't really care," Federer said. "I'm an active athlete right now, and it's not fun times really to be in sports to a degree."
Serena Williams said Armstrong let all athletes down by doping and lying about it for so long, while top-ranked Victoria Azarenka says the disgraced cyclist "deserves everything he gets."
"I think a lot of people now look and are like, 'OK, if somebody (is) that great, what about everyone else in every other sport?'" Williams said.
"As an athlete, as someone that works really, really hard since I was 4 or 3, I think it's a sad day for all athletes in general. Overall, it's even more disappointing for the people that were adversely affected through everything. You can only just hope for the best for them."
Azeranka said "everybody works so hard to be the best."
"You cannot be a hero in the end of the day," Azeranka said. "You cannot lie. You cannot cheat. Everybody works so hard to be the best, and you have to respect that."
On Friday, No. 1 Novak Djokovic said it was a "disgrace for the sport to have an athlete like this" and that Armstrong should "suffer for his lies."
In the second half of his televised interview with Oprah Winfrey on Friday night, Armstrong said he lost $75 million in sponsorship deals after his doping use was revealed.
In the first part, broadcast Thursday, Armstrong admitted he used drugs such as blood-boosting EPO when he won seven straight Tour de France races. Armstrong was subsequently stripped of his Tour titles, as well as an Olympic bronze medal he won in the road time trial at the 2000 Sydney Games.