After an outstanding 2014/15 campaign, the midfielder was one of several players who struggled last campaign as the Blues had a disastrous season.
He has been linked with a move away from Stamford Bridge with reports suggesting Juventus are lining him up as a replacement for Paul Pogba, who is believed to be on his way to way to Manchester United.
However, Conte insists the 27-year-old is not for sale.
"He is not for sale and I know with work he can become a fantastic midfielder, one of the best in the world," he told The Telegraph.
"He is a very important player for me, he is very important in my idea of football. He knows this and I’m delighted by his attitude and behaviour and I see in him commitment."
The acquisition of N'Golo Kante from Leicester City means Chelsea are now well stocked in midfield.
"N'Golo, Nemanja, Cesc [Fabregas], Oscar, [Nathaniel] Chalobah and [John Obi] Mikel, who is in the Olympics, it is not easy to choose. I want to have this problem," Conte told Sky Sports.