Nadal hustled his way into a 13th Australian Open quarter-final appearance with a 6-3 6-4 6-2 win over Fabio Fognini on Monday - with the back injury that ruled him out of the ATP Cup now almost a distant memory.

Now, the focus is firmly on whether the world No.2 can snare the major that will push him one ahead of Roger Federer - even if Nadal himself played down his ambitions of a second Melbourne Park triumph.

"Of course I am (motivated by winning grand slams) but I am not obsessed," Nadal said.

"I play tennis. I like tennis. I like what I am doing. That's the main thing.

"I mean, of course I am very motivated to win grand slams and to play in the most important events of the year. No doubt about that.

"The only thing that I said is I have never been obsessed to try to be the best ... no, I just did my way. That worked for me."

If the 2009 champion is again triumphant in Melbourne, he will also clinch a long-elusive milestone: becoming the first man in the Open era to win all four grand slams twice.

But Nadal instead stressed his focus on having a "healthy" ambition and knowing he "gave it everything' each match.

"If you have too much ambition then you can be frustrated when you are not able to achieve all the things that you wanted," he said.

"I never approached the sport and my career that way. That's it."

Nadal will play fifth seed Stefanos Tsitsipas in the quarter-final after ninth-seeded Italian Matteo Berrettini withdrew from Monday night's fourth-round clash with an abdominal strain.

The world No.2 said he'd recently trained for two days in a row for the first time since suffering his back injury and was confident his physical condition was improving each round.

After winning the first set against Fognini - which he described as his best tennis of the tournament to date - Nadal slumped to a 4-2 deficit in the second.

But the Spaniard reeled off four consecutive games to win the set and kicked on to beat Fognini in straight sets.

"I made a step forward today, something that I needed, and I need to make another one for Wednesday," Nadal said.

Australian Associated Press