The two-time grand slam finalist has been impressed by Kyrgios' improved fortunes on and off the court this summer, declaring him a "good kid".

But Philippoussis said Kyrgios needed to start regularly taking more scalps in order to snatch his maiden slam.

It comes a day after seven-time grand slam winner Mats Wilander said Kyrgios could win up to five majors.

But the 24-year-old hasn't made a quarter-final at a major in five years, with just two fourth-round appearances since 2015.

That could change if he upsets world No.1 Rafael Nadal on Rod Laver Arena on Monday night.

"He has the ability to win multiple slams, but in order for that to happen, you've got to make tennis your absolute priority," Philippoussis told reporters.

"A lot goes into a grand slam...it's a lot of tennis.

"You need to be prepared, a little bit lucky, there's a lot of things that have to come into play in order to win one.

"But let's first start off with getting deep in the second week, start off putting yourself to win that first one is very important."

Philippoussis' career wound down around 2006, having never won a major, losing finals at the US Open in 1998 and Wimbledon in 2003.

The former world No.8 says tennis may not be the most important thing in Kyrgios' life and family could be his priority.

"I can't speak for anyone else, but Nick's a good kid, he's a good guy," he said

"At some stage tennis is going to be finished and then it's going to be about life. That's what it's important.

"This is one stage of his life so it's about whatever makes him happy."

Australian Associated Press