Italy international defender Davide Astori died in his hotel room on Saturday night after a "sudden illness", his club Fiorentina said on Sunday.
"Fiorentina are profoundly shocked to have to announce the death of captain Davide Astori after a sudden illness," the Serie A club said on Twitter.
Astori, who leaves behind a two-year-old daughter, was in Udine to prepare for Sunday's match against Udinese, who announced the game has been postponed. Serie A have since announced that all scheduled matches on Sunday have been postponed.
When Astori's death was announced on the stadium video screen, many of the players warming up walked off the field.
Astori began his career at AC Milan, also playing for Cagliari and Roma before joining Fiorentina in 2015. He played 14 times for Italy.
Players and clubs from around the world have taken to social media to offer their condolences.
"A man who loved football and who grew up as footballer with us," AC Milan wrote on their Twitter account. "AC Milan are shocked by the passing of Davide Astori. It is with great sadness that we offer our deepest condolences to his family and closed ones and to ACF Fiorentina."
Roma, with whom Astori spent a spell on loan in 2014/15, wrote: "The club is devastated to learn of the death of Davide Astori. The thoughts of everyone at AS Roma are with the player's family, friends and teammates at this terrible and tragic time."