Hazard has already scored six goals in seven Chelsea appearances this season, including Wednesday’s sublime solo strike to seal a 2-1 win at Liverpool in the League Cup third round.
The 27-year-old’s fine form has seen some pundits rank him alongside Barcelona great Lionel Messi and Juventus forward Cristiano Ronaldo.
But Sarri insists Hazard isn’t there yet because he can still add another layer to his game by training with even more desire and drive.
“I think that he is for sure one of the best (players in the world), but I am absolutely convinced that he can improve,” Sarri told reporters on Friday.
“If he’s able to improve during training maybe he will be able to use and serve at 100 percent.
“Because I think that we have seen only 75, 80 percent of his potential.
“So I think that if he’s able to improve he will be the best in the world.”
Hazard has another chance to showcase his class on the big stage when Liverpool visit Stamford Bridge in the Premier League on Saturday.
Table-topping Liverpool has won all six of their league games, while unbeaten Chelsea is two points behind.
A Chelsea victory would be a major statement of intent and they are sure to need Hazard at his best to kill of Jurgen Klopp’s side.
Asked if Hazard could be voted the best player in the world in a year’s time, Sarri said: “I think so, I think so.
“It’s very difficult to compare him with other players. He’s a genius. He’s unique.
“He’s a genius, technically I think he’s the best. And so I want him to be the best in the world.
“More continuity from the physical point of view, from the mental point of view.
“Because he has the opportunity to improve more, and he can become the best player in the world.
“It’s a very interesting challenge I think. He has a lot to give, to the team, to the staff. And I want everything.”
Meanwhile, Gary Cahill has admitted he may have to leave Chelsea in January and go in search of regular first-team football.
Cahill has hardly played this season, but Sarri has urged the former England defender to bide his time before making any decisions.
“I have spoken with him but I think that there is October, November, December, so I think that he has to wait,” Sarri said.
“And then we have to wait. I repeat I was really very happy with the performance of Cahill (at Liverpool on Wednesday).
“And so now Gary for me is very useful. January is far from now, so we will see.”