Former AC Milan CEO Adriano Galliani has described Davide Astori as "one of our boys", as officials await the results of an autopsy.
The Fiorentina captain, who came through the youth system at Milan, was found dead in his hotel room early on Sunday, just hours before his side were due to face Udinese away from home.
No cause of death has yet been identified, and Udine's public prosecutor Antonio De Nicolo confirmed to Radio Rai on Monday that criminal proceedings had been opened "on the hypothesis of manslaughter against unknown persons".
The manslaughter process is understood to have been initiated to allow a full autopsy to take place and is not currently linked to any individual, with De Nicolo describing the theory as "purely abstract", according to ANSA.
On Sunday, De Nicolo stated it was likely Astori "died of cardiac arrest by natural causes", adding it was "strange for a professional so closely monitored and with no warning signs".
Astori spent five years with Milan's youth set-up before leaving for Cagliari in 2008, where he became a fan favourite.
Although he never played a senior game for Milan, Galliani remembers him fondly and is heartbroken at the thought of him having left behind a young daughter.
"I remember him really well," Galliani, who was Rossoneri CEO from 1986 until 2017, told Tuttosport. "He came to us in 2001 and he went through all the youth tiers with us.
"He was a polite, clever and punctual boy. Even when very young, he had the characteristics of a professional.
"Everything that's happened is shocking. I feel like crying knowing that he has left a wife and a two-year-old daughter, who will grow up not knowing her dad.
"He was one of our boys, who had the Milan style."
All Serie A and Serie B matches on Sunday were postponed as a mark of respect for Astori.
Tributes have come in from across football, with Gianluigi Buffon, Leonardo Bonucci and Chelsea boss Antonio Conte among those to pay their respects.