"He taught us to think differently and to have the courage to change, often in unconventional ways, always acting with a sense of responsibility for the companies and their people", he said of Mr Marchionne.
Marchionne, 66, had already announced he would step down in early 2019, so the board's decision, to be confirmed at an upcoming shareholders' meeting, will "accelerate" the CEO transition process, the statement said.
Mike Manley talks about the 2017 Jeep Compass at Los Angeles Auto Show in 2016 as head of the Jeep brand.
Elkann didn't give details of Marchionne's health problems, adding that his "first thoughts go to Sergio and his family".
Elkann said, "What struck me about Sergio from the very beginning, when we met to talk about the possibility of him coming to work for the Group, even more than his management skills and unusual intelligence, were his human qualities, his generosity and the way he understood people".
Elkann, who is the grandson and chosen heir of former Fiat boss Gianni Agnelli, issued the following statement.
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Having denied Russian interference in the election and the possibility that the Russian government may have blackmail on Mr. His comments drew widespread, bipartisan condemnations in the USA , with several critics calling them " disgraceful ".
He is also chairman and CEO of Exor, an investment company controlled by the Agnelli family, which controls Ferrari, Partner Re, CNH Industrial and Juventus F.C.
Analysts questioned whether new CEO Louis Camilleri would be able to do the same and grow Ferrari beyond what it is today while keeping dealers, racing fans, owners and collectors on board.
Fiat Chrysler Automobiles CEO Sergio Marchionne has experienced "unexpected complications" following surgery.
Marchionne, a dual Italian-Canadian citizen with an MBA from the University of Windsor and a career mostly in Europe, was picked to lead Fiat in 2004.
This has also prompted succession plans at sportscar maker Ferrari and truck and tractor maker CNH Industrial, spun off from FCA in recent years.
Manley was appointed head of the Ram brand in 2015. Those brands were expected to account for 80 percent of revenues by 2022, compared to 65 percent now. FCA's success has been anchored by Ram and Jeep, although the company has been less successful in the United States with Fiat, Alfa Romeo, and Chrysler.
At the June appearance, Marchionne also predicted Fiat was about to eliminate its debt.