Davide Astori was due to sign a new contract with Fiorentina on Monday which would have tied him to the Serie A club for the rest of his career, according to the club's president Andrea Della Valle.
The 31-year-old defender died in his sleep overnight on Sunday with an autopsy due to determine the precise cause of death.
Fiorentina's fixture at Udinese on Sunday was called off along with the remainder of the Serie A weekend programme as Italian and world football mourned the unexpected loss of a player who Della Valle revealed was set to make the city of Florence his permanent home.
"Believe me, it is hard to be here," Della Valle told reporters outside Fiorentina's headquarters on Sunday after the team returned from Udine. "This is a huge tragedy for us. I don't even know how to express this pain. We are all under shock.
"He was with us for four years and just think that he was due to extend his contract on Monday. He was due to do it earlier, but due to the snow, we had put it back and agreed we would do it on Monday. It was his greatest joy to be able to end his career here, because this is where it would have ended."
The mayor of Florence has announced that a day of mourning will be held on the day of Astori's funeral, a date for which is yet to be set, with a memorial to be built "to remember Davide and enhance, through his figure, the clean, correct and human image of football and sport in general."
"The news of the premature death of Davide Astori has shocked the world and distressed the whole of Florence, the city he had chosen to pursue his profession in and for his family life," wrote mayor Dario Nardella in a statement.
"The role of captain of the city's club, the deep bond he knew how to create not only with the fans but with an entire community thanks also to the undoubted human qualities and civic values he showed he believed in, the exemplary conduct of professionalism attached to the most authentic of values of the Viola and Italy national team shirt and the world of sport in general and, last but not least, the young age in which he has been taken by a tragic, unexpected death form the basis of a collective feeling of grief on the part of the entire city of Florence.
"The mayor announces a day of mourning on the day of the funeral of Davide Astori, an exemplary man more than a footballer."
Giovanni Malago, acting head of the Lega Serie A and president of the Italian Olympic Committee, said there was no alternative but to postpone all of Sunday's league fixtures in Italy.
"I spoke with all the clubs' presidents and they all agreed," he said at a news conference. "The football that I imagine is one of values, ideals and the sharing of emotions and respect -- not only as athletes, but also as humans. This was necessary.
"Often they say that the show must go on, but that does not matter for me. Football is the most popular sport, but also one which must give clear signals in a moment like this."
While the Italian football programme was postponed, Antonio Conte -- who had picked Astori when he was coach of the Italy national team -- had to sit on the bench for Chelsea in their 1-0 defeat to Manchester City.
He wore a black armband as a show of respect and said after it had been difficult to focus on the game.
"It's very hard to talk about football after this tragedy," he told Sky Sport Italia. "He was a fantastic lad with healthy principles and healthy values. He was a great player and I had the pleasure of having him in the national team.
"He was only 31 and this tragedy hurts because I had the fortune of knowing Davide, who was an exceptional lad. I'm so sorry for the parents, the wife, the daughter -- it's devastating. It's devastating and you can't find a reason for it or find the right words in a moment like this."
Chelsea and many other clubs from around the world expressed their sympathies, but Ciprian Tatarusanu, a former teammate of Astori at Fiorentina, felt not enough solidarity was shown, as he was forced to keep goal for Nantes in their Ligue 1 fixture with Marseille.
"It was the worst day of my life," RMC Sport reported him as saying. "There was not even a minute's silence after the death of my former teammate Davide Astori. It's a scandal and a lack of respect. After such a shock, the result of a football match is only secondary. They are only games and there will be many more."
Tatarusanu played with Astori for two seasons before moving to Nantes last summer.