Ivan Turina, goalkeeper of Swedish top-flight club AIK, was found dead in his Stockholm apartment on Thursday. He was 32.
"It is with great sorrow and shock that we can confirm that goalkeeper Ivan Turina passed away on the night between Wednesday and Thursday," the club said in a statement.
"Ivan died suddenly in his sleep and at the moment no crime is suspected."
Club chairman Johan Segui later added in newspaper Expressen: "We knew that he had a congenital heart problem but he was completely healthy."
AIK striker Henok Goitom, who lived next door to Turina, later expressed his sorrow to reproters at the club's training ground.
"Yesterday was an ordinary day. Today, Ivan is dead. It's a shock," he said. "The AIK supporters loved him. It's a slap in the face for everyone but we are united as a group and we're trying to help everyone in AIK and his family."
Turina joined the club, based in the Stockholm suburb of Solna, in 2010 from Dinamo Zagreb, where he had spent the majority of his career.
He soon became first choice at the club, and went on to make 65 league appearances for them.
Turina, who made his one and only senior international appearance for Croatia in 2006, is survived by his wife and two one-year-old daughters.