Ivory Coast international Cheick Tiote "suddenly fainted" at training and died later in hospital, his Chinese club said on Tuesday, as tributes flooded in for the player.
Tiote, 30, who had only moved to China in February from England's Newcastle United, collapsed at training on Monday, second-tier Beijing Enterprises said.
He was rushed to hospital where he died, the club said, describing his death as "tragic" and praising his skills and attitude.
"Tiote has made outstanding contributions to the club and earned high praise from his coaches and team-mates for his superb football skills and professional attitude," the club said, adding it has been in touch with the his family.
Tiote was well known in English football circles after a seven-year stint with Newcastle, including six Premier League campaigns before their relegation last year.
The popular, tough-tackling midfielder is well remembered for his crunching left-foot volley from 25 yards to secure a 4-4 draw with Arsenal in 2011.
Tiote was also part of the Ivory Coast squad that delivered the 2015 Africa Cup of Nations after a 23-year drought.
Earlier this year he became one of a number of players -- including several high-profile acquisitions -- to move to Chinese teams.
Several footballers have died in similar circumstances including Cameroon's Marc-Vivien Foe, who collapsed during a Confederations Cup match in 2003 and died from a previously undiagnosed heart condition.
I loved him
Newcastle said in a statement they were "devastated" about Tiote whilst Alan Pardew, who managed him at Newcastle, said he "loved" the player.
"From the moment I arrived at Newcastle, Cheick was a wonderful presence around the dressing room and his performances on the field often defied belief," Pardew said in a statement, quoted by independent.ie.
"I loved him. He's everything that you want in a Newcastle player."
Fellow Ivory Coast player Gervinho, who plays for Hebei China Fortune, described Tiote as a "warrior" and "champion" in a Twitter post.
"May your soul rest in peace," he said.
Brazil's Oscar, who moved from Chelsea to Shanghai SIPG this Chinese Super League season, tweeted: "Rest in peace, Cheick Tiote. My family prays for your family."
Tiote was capped 52 times by Ivory Coast and was in their squads for both the 2010 and 2014 World Cups.
He began his European club career with Belgian outfit Anderlecht and had a loan spell at Roda JC Kerkrade before moving to FC Twente in 2008.
Tiote signed for Newcastle in 2010 and made 156 appearances for the club, becoming a firm favourite with fans.
"The thoughts of everyone at Newcastle United are with Cheick's family, friends, team-mates and everyone connected with the clubs he represented," a club statement said.
Chinese fans also expressed their sorrow over Tiote, who grew up in poverty as one of 10 children and didn't own a pair of football boots until he was 15.
"I hope there is football in heaven," said one user on China's Twitter-like Weibo.
Another said: "Although I'm not a fan of Beijing Enterprises club, we are both people who love football and I feel sorry for him."
Rival club Tianjin Quanjian also expressed "its deep condolences", while Shanghai SIPG said it was in "mourning" over the talented player's death.