Zverev is the current world No 3 and he is heavily tipped to step into the shoes of Roger Federer and Rafael when they call time on their careers.
The German reached his maiden Grand Slam quarter-final at the French Open but ran out of steam after being forced to go the full five-sets over the previous three rounds.
The youngster’s failure to have ever been beyond the last eight means he has never had a shot at winning a major competition.
And Austin warns that Zverev must improve his performances in the big events if he is to ever reach the top.
“He is No 3 now and he is behind by a lot of points,” Austin told Tennis Channel.
“It is 2,800 points and Nadal and Federer are courting up all of those Grand Slams.
“But I am thinking that Rafa this time next year will be 33 and Roger in a year will be 38 so maybe father time will start to catch up with him and Sacha will go deeper in the Slams.
“That’s what he has to do to even touch the No 1 ranking in the next year and a half.”
Meanwhile, fellow pundit Justin Gimelstob believes Zverev has come on a long way since the turn of the year.
“I think he has made progressions winning those three five-set matches and he has obviously proved himself at the highest level of Masters 1000, winning a bunch of them,” he added.
“Roger and Rafa might slow down a little bit. He could maybe play a little bit more selectively and Zverev is viable on all surfaces.
“He is young, he is hungry and he is definitely going to be a world No 1 at some stage as long as he stays healthy.
“He is going to be a future of the sport with a few of these other guys.”
Source : EXPRESS