Sergio Marchionne's resignation from the top post at Fiat Chrysler Automobiles on July 21 due to health reasons and his subsequent death four days later came as a shock to many, including close employees at the automaker he ran.

This is despite Marchionne having had received treatment from University Hospital Zurich for more than a year, which the Swiss hospital confirmed on Thursday.

Italy's Lettera43 reported Tuesday that Marchionne underwent surgery at University Hospital Zurich for an invasive shoulder sarcoma and had suffered a cerebral embolism during the procedure, which plunged him into a coma.

A spokesman for FCA told Reuters in an interview published Thursday that the lack of knowledge of Marchionne's poor health was due to medical privacy. He revealed that FCA only learned from family members on July 20 that Marchionne would be unable to return to work due to serious complications following surgery he had undergone at University Hospital Zurich.

FCA announced the news the next day and named Mike Manley, who at the time headed the Jeep and Ram brands, as its new CEO. Replacements for Marchionne's chairman and CEO roles at Ferrari were also announced the same day. 

Bloomberg reported Thursday that University Hospital Zurich only broke with protocol of withholding patient information to dispel rumors in the media about Marchionne's medical treatment. Marchionne was 66 when he died. He was due to retire next year.

During the past 15 years, Marchionne saved both Fiat and Chrysler, a task that often saw him working seven days a week. Last month, FCA paid off its net industrial debt, which was part of a larger plan to spend billions on new cars and technologies by 2022. Revealed earlier this year, the five-year plan calls for several new models and a major push into self-driving and electrification technologies.