Puerta, aged 22, died four days after suffering a heart attack while playing for Sevilla against Getafe. Since then, the Spanish sporting authorities have tried to be more aware of the possible heart problems of footballers and other sportsmen.

In October 2008, Real Madrid's Ruben de la Red, 23, collapsed during a King's Cup match against Union Irun and had to be rushed to hospital with a suspected heart attack. He has not played since while club doctors strive to determine the nature and extent of his problem.

'This is really horrendous,' said Espanyol technical secretary German de la Cruz Sunday,' it is something that we just cannot understand.'

There was a minute's silence for Jarque during Saturday night's friendly between Valencia and Arsenal. After the match Valencia star David Villa said that 'we are all really upset at this ... Daniel was a good person and a great player.'

Real Madrid captain Raul said Sunday: This unexpected news has left us consternated and tremendously sad ... It is a pity for football.'

Ernesto Valverde, who guided Espanyol to the 2007 UEFA final and is now coach of Villarreal, said on Sunday that 'this has been a really disagreeable piece of news. Daniel was a healthy boy and extremely strong. It is incredible that this has happened.'

Meanwhile, Barcelona president Joan Laporta said that 'we are very sorry about this. Today we are all in mourning.'