Ivan Turina, goalkeeper for Swedish club AIK, has died at the age of 32.
The Croatian is thought to have passed away in his sleep on Wednesday night, with no suspicious circumstances.
AIK chairman Johan Segui said: "We knew that he had a congenital heart problem but he was completely healthy."
Turina, who won one cap for Croatia seven years ago in a friendly against Hong Kong, joined AIK from Dinamo Zagreb in 2010 and went on to make 89 appearances, keeping 35 clean sheets.
He also previously had spells with Greek side Skoda Xanthi and Lech Poznan of Poland.
A club statement said: "AIK Football thoughts go out to Ivan's partner and two daughters and his other relatives and friends.
"AIK Football has informed the team and other employees about what happened.
"We ask all to respect all parties and allow them to mourn in peace."
Turina had agreed a new contract until 2016 with the club during their pre-season trip to the Unites States in February.
His wife is expecting the couple's third child.