By Alastair Macdonald
BRUSSELS (Reuters) - Belgium under-21 international Gregory Mertens died on Thursday, three days after collapsing with heart failure during a match, a spokesman for his club, Lokeren, said.
The 24-year-old defender had been in a coma since going into cardiac arrest early in a reserve team game on Monday.
Club spokesman Herman Van De Putte told Reuters that his condition continued to worsen and the player's family had agreed with doctors to switch off the life support system.
"Much too soon must we bid farewell to Gregory Mertens," the club said in a statement. "We are a football (soccer) club. Everyone in and around the club breathes football. But suddenly something happens where we realize football is just football.
"Today is such a time ... The medical team did all they could to save Gregory but in the end had to recognize their impotence. Gregory passed away today about 4:30 PM (1030 EDT).
"His family were able to say their farewells."
Mertens, who joined top-flight Lokeren last summer after nearly 100 appearances for Cercle Bruges, collapsed 15 minutes into the game at Racing Genk and despite lengthy efforts to bring him round doctors quickly said his survival needed a "miracle".
The death of a young man his club described as making himself "indispensable" while never losing his "quiet modesty" shocked many leading figures across European soccer.
Chelsea's Belgium international goalkeeper Thibaut Courtois tweeted in Dutch: "RIP Gregory Mertens! Much strength to family and friends."
Fabrice Muamba, who as a 23-year-old nearly died during an FA Cup match in England three years ago, tweeted: "Horrible news that Gregory Mertens has passed away, only 24 years old. #RIP."
A former England Under-21 international, Muamba's heart stopped for over an hour during a televised quarter-final for Bolton Wanderers at Tottenham Hotspur.
He survived and retired from the game, drawing attention to the health risks young players can face.
"Shockingly sad," former England striker and television presenter Gary Lineker tweeted after news of Mertens' death.
Manchester City said: "Our thoughts are with the friends and family of @KSCLokeren's Gregory Mertens at this sad time."
(Reporting by Alastair Macdonald and Miranda Alexander-Walker, editing by Pritha Sarkar and Toby Davis)