Cape Town - Former Australian tennis sensation Mark Philippoussis believes rising German star Alexander Zverev will continue to struggle in Grand Slams unless he changes his reliance on energy-draining baseline tennis.

Zverev, the current world No 4, is seen as the young player with the best chance of ending the dominance of veterans Roger Federer, Rafael Nadal, and Novak Djokovic next season, having seemingly realised his potential with his impressive victory at the ATP Finals in London where he defeated Federer and Djokovic on the way to the trophy.

The young German has frequently underperformed in Grand Slams, however, with a quarter-final appearance at this year's French Open his only real achievement of note.

And while Philippoussis acknowledges that Zverev is the only player currently threatening the big three, he expects his Grand Slam struggles to continue unless he makes some changes to his game.

"The only guy who has stepped up is Zverev," the 2003 Wimbledon finalist told metro.co.uk. "But he hasn’t done it in Grand Slams yet.

"He’s far from done it at Grand Slams. He needs to step it up, starting at the Australian Open. His game is staying back on the baseline and that’s no problem but when you’ve got seven best-of-five set matches to win you need to, you know, kind of get through that first week without working as hard.

“In my opinion, he just stays three or four feet too far back behind that baseline and he’s just doing a lot of work. That’s fine in the best-of-three sets, the tournaments that he’s winning three or four of this year but in Grand Slams it’s just a different story. He’s working way too hard and he’s getting hurt by guys he just shouldn’t be getting hurt by. He’s just way too far back."