Fiorentina captain Davide Astori passed away due to a cardiac arrest, an autopsy has revealed.
The Serie A club confirmed on their official Twitter account on Sunday that the defender, 31, had tragically passed away.
Fiorentina were due to play Udinese in the Italian top flight but that game - along with all other Serie A fixtures - were called off.
And an initial autopsy has revealed that Astori most likely suffered bradyarrhythmia - meaning his heartbeat got slower and slower until it stopped - while he was sleeping from Saturday night into Sunday morning.
"Based on the evidence of the autopsy examination, carried out on March 6, 2018, on the body of Davide Astori, with reference to the cause of death, this cause can be indicated as of a cardiac nature, most likely a bradyarrhythmia with pluri-visceral congestion and a pulmonary oedema," Antonio De Nicolo, the chief prosecutor of Udine, told RAI television.
"From the preliminary results, it does not seem like there is any external causes other than that of a natural death, but prudently our advisors are telling us that we must wait for the result of histological examinations before making a definitive statement."
There will be further and deeper investigations into Astori's passing with the results expected in 60 days.
Italian authorities confirmed on Monday that they had opened manslaughter proceedings into the death of the 14-cap Italy international.
Under Italian law, the only way an autopsy could take place on Astori in order to discover the cause of death was to open such a case.
Astori started his career out at AC Milan, where he never played a Serie A match, before moving to Cagliari.
The centre-back turned out 174 times for the Sardinians in a six-year spell, during which he made his national team debut with Italy.
Astori was sent on loan to Roma in 2014 and then a year later made a similar transfer to Fiorentina, but with an obligation to buy at the end of the season.
Fiorentina and Cagliari have since announced that they will be retiring their No. 13 shirts in the wake of Astori's death.