Fernando Alonso was said to have lost faith in
Ferrari's inability to produce a winning car. With three races of the
championship remaining, he sits third in the drivers' championship
standings.
Former two-time world champion Alonso was widely rumoured to be leaving the Italian giants at the end of the current season, two years before his contract ends.
De Montezemolo, who recently quit his post as president of the company, confirmed to Italian television Rai that the Spaniard was leaving "for two reasons".
"He's leaving for two reasons. One is he want to test himself in another environment, and two because he's at an age where he can't wait much longer if he wants to triumph again."
Alonso was said to have lost faith in Ferrari's inability to produce a winning car. With three races of the championship remaining, he sits third in the drivers' championship standings.
"It hurt him that he didn't win this year and he needs fresh motivation," added De Montezelomo.
Alonso's contract with Ferrari was set to expire at the end of 2016, meaning he would leave two years short of its expiry.
While speculation over the Spaniard's future destination continues, four-time world champion Sebastian Vettel of Red Bull is rumoured to be heading to Ferrari.
Vettel announced last week he was quitting Red Bull.
