From Wikipedia:
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On January 25, 2004, Benfica travelled to Guimarães to play Vitória S.C.. The game was being broadcast live on television, and Benfica were leading 1-0. Fehér, who had just come on as a substitute and assisted another player brought from the bench, Fernando Aguiar, for the match’s only goal, received a yellow card in injury time and suddenly bent forward, seemingly in pain. He then fell backwards to the ground.
Teammates rushed immediately to aid Fehér before medical personnel arrived on the pitch. CPR was performed as players looked on in visible distress. An ambulance arrived on the pitch, and Fehér was rushed to the hospital. His condition was covered by the Portuguese media throughout the day. However, before midnight, Fehér’s death was confirmed. The Public Prosecutor (the Portuguese agency responsible for the release of autopsy details) announced that Fehér died of a heart attack. He was only 24 years old.[2]
In his memory, Benfica retired the number 29 shirt, which he wore during his time at the club. This number will never be worn again by any club player. He was remembered by many, and his death caused a profound shock in Portuguese sports. Among others, Reinaldo Teles (director of football of FC Porto) and José Mourinho (Porto’s manager at the time) paid their respects at the Estádio da Luz where the player’s body remained before his burial in native Hungary.
A club delegation, which included the entire squad, travelled to Hungary, presenting Fehér’s parents with the 2004-05 league championship medal, in respect for the player and his time with the club.[
