Mark Philippoussis compared Nick Kyrgios to a fledgling NBA player struggling to fulfil their potential ahead of the Australian Open as he urged the Australian star to become physically and mentally stronger in his pursuit of a maiden grand slam.

Kyrgios is full of confidence leading into next week's Australian Open after claiming the Brisbane International – his fourth ATP title and first since October 2016, having finished runner-up twice last year.

With fitness concerns over world number one Rafael Nadal and Novak Djokovic following the withdrawal of five-time runner-up Andy Murray as well as Kei Nishikori, this year's tournament in Melbourne looms as an opportunity for Kyrgios to break through for his maiden major.

The 22-year-old, however, has come under scrutiny in recent years for his antics both on and off the court, casting doubts as to whether he has the mental capacity to become a tennis great.

That is why countryman Philippoussis – a Wimbledon and US Open finalist – has tipped Germany's Alexander Zverev to go onto achieve more than Kyrgios, impressed by his attitude and sustained will to win.

"You look at some other sports - NBA players, there's some guys who are supposed to be the next big thing and are so incredibly talented that they do amazing things, but it just doesn't happen," Philippoussis, 41, told Omnisport.

"I hope he [Nick Kyrgios] doesn't get into that category, but then there's somebody like Zverev. The kid's talented, maybe not as talented, but he wants it. You can see he's hungry and you can see he wants it on the court. He's training and he's competing out there, and that's just the difference in my opinion.

"It's different playing one or two matches and being up for one or two matches, but for a grand slam you need to be up to win seven matches that are best-of-five [sets] for two weeks. That's a different story.

"The [Davis Cup] semi-final tie against Belgium was... we had the opportunity. Kyrgios should hold his head up high. He played great those first couple of days and competed well. You just want to see that on a day-to-day basis that's all. It's like you see it and you know what he's capable of, so then you just want that for him going into the big grand slams, when you've got a day off between the matches.

"At the end of the day it's up to him. It's whatever makes him happy. He loves representing his country without a doubt and he's very excited and up for it. There's a lot of passion on the court and it's great to see. I just hope it carries on to the grand slams."

Asked how far away is Kyrgios from challenge the best in the sport, Philippoussis said: "Very far. Very far, to be honest.

"Yes, he has an incredible amount of talent, but lets be honest, that doesn't matter. For the top players, everyone is talented. When it gets to that certain point, it's about who wants it more, who's willing to train harder, and whose physically and mentally stronger, especially in the grand slams.

"He'll continue to win tournaments, absolutely. He could even get into second week of grand slams. But will he have opportunities to get through to semis or past the quarters into the semis, yes, but he hasn't been physically strong enough to do that or mentally. And that's just going off results and what I've seen. It's nothing against him.

"I've always been very vocal as someone, as far as supporting him, but if you want me to be honest, everyone will just say the same thing because it just comes down to... forget the talent, we all know he has the talent, but after a while that doesn't matter anymore."