"Marchionne, the end of an era," was Corriere della Serra's headline after an emergency board meeting of Fiat Chrysler (FCA), Ferrari and CNH Industrial, the three groups controlled by the Agnelli family, who met Saturday to announce the end of his tenure.
Marchionne, 66, suffered serious complications following surgery on his right shoulder last month and La Repubblica said his condition was giving cause for major concern.
The paper said there had been a further "deterioration" in his condition Friday and that "this time there is no return -- the patient is no longer responding" to treatment.
The hospital treating him would not comment when contacted by AFP, citing patient confidentiality.
"This is terrible news," said Marco Bentivoglio, general secretary of the CISL metalworkers union. "We have not seen eye to eye on certain things... but together we challenged little lazy Italy which prefers to close plants rather than roll up its sleeves."
In his 14 years at the helm, Marchionne revamped Fiat, Italy's premier private enterprise, from top to bottom turning it into a sector mastodon, merging it in 2009 with US automaker Chrysler, then hiving off its industrial vehicles to create CNH Industrial in 2011 before a successful spinoff of luxury brand Ferrari in January 2016.
Some politicians joined the media in eulogising Marchionne, including former centre left prime minister Matteo Renzi.
"Marchionne has been a great protagonist of economic life for the past 15 years... he has succeeded in giving Fiat a future when that seemed impossible. He created jobs, not unemployment. I take my hat off to him," said Renzi.
Marchionne was close to Renzi for some years before keeping his distance later, albeit he did not go as far as taking up a suggestion by another former premier, media magnate Silvio Berlusconi, to head up a conservative coalition in the March legislative elections.
Italy's new coalition government was discreet in its reaction to Marchionne's departure and passing of the torch to Briton Mike Manley, previously head of the group's Jeep brand.
Far-right Interior Minister Matteo Salvini offered Marchionne his "recognition and respect along with best wishes" for a recovery.
As speculation continued on his health media speculated on the future for Fiat.
For Dario Di Vico, editorialist at Corriere, Marchionne had "incarnated in the history of our country the very idea of modern industry."
But he expressed concern "for the life of one of the world's most highly-regarded managers" as well as posing "legitimate questions on the future of the world's seventh-largest automaker."