Rafael Nadal is unsure whether he likes Nick Kyrgios ahead of a potential last-16 clash at the Australian Open amid the pair's tense relationship.

World number one Nadal raced through to the fourth round at Melbourne Park thanks to Saturday's ruthless 6-1 6-2 6-4 victory over fellow Spaniard Pablo Carreno Busta.

Next up for 19-time grand slam champion Nadal is either maligned Australian Kyrgios or Karen Khachanov in Melbourne.

All eyes have been on Nadal and Kyrgios since the latter described the Spanish superstar as "salty" last year, after the duo exchanged words at the 2019 Mexican Open.

That feud has been thrust into the spotlight after Kyrgios impersonated Nadal – who has called for the 24-year-old to show more respect – as he was called for a time violation during his second-round win against Gilles Simon at Melbourne Park.

Nadal was asked about Kyrgios following his match on Rod Laver Arena and the 2009 Australian Open champion's response was telling.

"I don't know. I don't know him personally, honestly, to have a clear opinion," Nadal told reporters when asked if he liked Kyrgios. "It's clear, of course, that when he does stuff that in my opinion is not good, I don't like. 

"When he plays good tennis and he shows passion for this game, he is a positive player for our tour, and I want my tour bigger, not smaller.

"So the players who make the tour bigger are important for the tour. When he's ready to play his best tennis and play with passion, is one of these guys. When he's doing the other stuff, of course I don't like."

Nadal produced a breathtaking and efficient display of tennis against Davis Cup team-mate Carreno Busta, hitting 42 winners and just seven unforced errors under the Melbourne sun.

The four-time Australian Open runner-up needed just one hour, 38 minutes to reach the last 16 of a slam for the 47th time in his career.

"It was my best match of the tournament so far, without a doubt. Big difference between today and the previous days," Nadal said. "I have been serving well, starting to create damage with the forehand. Hitting serve on one shot, I think."