Sevilla's Spanish international defender Antonio Puerta died on Tuesday after suffering a heart attack during a Spanish league match on Saturday.
The 22-year-old had been in "very critical" condition in the intensive care unit of Seville's Virgen del Rocio hospital where he had been hooked up to a life support machine, the hospital said earlier in a statement.
Puerta collapsed after half an hour of Sevilla's 4-1 win over Getafe on the opening day of the Spanish season.
He was able to walk gingerly to the dressing rooms where he collapsed a second time before being taken to hospital.
In January 2004 Benfica's Hungarian international striker Miklos Feher died during a Portuguese league match from a heart attack just seven months after Cameroon international Marc-Vivien Foe collapsed and died while playing in the FIFA Confederations Cup in France.
Earlier on Tuesday, the hospital had said: "The clinical evolution of the patient is unfavourable," citing prolonged cardiac arrest which had damaged Puerta's organs and led to a lack of oxygen to the brain.
The Spanish Football League (LFP) announced that next Monday's league match between Sevilla and Osasuna had been postponed as a mark of respect.
"The Spanish professional league wishes to pass on its most sincere condolences to the family of Antonio Puerta of Sevilla and to all connected with Sevilla," the LFP said in a statement.
"The LFP has declared an official day of mourning for the next round of matches and has asked all affiliated clubs to maintain a minute's silence before games," the statement concluded.
Sevilla also immediately sent a request to European football's governing body, UEFA, for Tuesday's UEFA Champions League return leg against AEK Athens in Greece to be postponed. This request has been quickly granted.
Puerta's reputation had blossomed in recent months with Sevilla's European runs - they also won the UEFA Cup in 2006 - and according to recent British media reports both Arsenal and Manchester United of the English Premiership had run the rule over the youngster.