The Swiss sensation issued the warning after easily beating Richard Gasquet 6-2, 7-5, 6-4 in just under two hours to reach the last 16 in Melbourne.
Federer won 12 months ago on his return after six months out from injury, with many assuming the 36-year-old was no longer a Grand Slam threat. But having seen off the Frenchman he claimed he was in much better shape than a year ago and ready to win Grand Slam No. 20.
“I had a good season last year,” Federer said.
“The off-season was fantastic too and my last match was not that long ago.
“I’m coming in this year very fit, very well equipped knowing that five sets are not an issue, where as last year that was always the question mark.
“And with that question mark in mind there was always a tension there and I was carrying a groin injury for the last four or five matches because it was so intense.”
The Swiss has only lost twice to the stylish Frenchman in their 19 meetings, winning all their four Grand Slam encounters.
Significantly, Gasquet has not won a set against Federer since 2011, a run of 22 sets to the Swiss.
"I was able to stay more on the offensive than he was and maybe I was protecting my own serve better than him," Federer said.
"I was hoping I could play at that level. I'm very happy that I was able to rise to a level that I needed to beat Richard.
"It was tough. The score shows it, as well. I could have done it maybe a bit faster.
"At the same time I'm happy to have done it the way it happened. I was pleased. I think I had some good shots. I was happy the way I played. I also thought we both played a good level again, so it was fun."
Elsewhere, Novak Djokovic played down injury concerns after he sought a medical timeout for a lower back injury during his 6-2, 6-3, 6-3 win over Spanish 21st seed Albert Ramos-Vinolas.
The former world No. 1 sought a medical timeout early in the second set for treatment to his lower back.
Djokovic later played down the extent of the problem, saying: “It’s okay. Nothing major. I knew I wanted to use the medical timeout because I needed it,” he said.
“But at the same time I knew it was nothing major that can potentially raise a question mark on whether I can continue playing or not. It was fine.”