Iker Casillas played 167 times for Spain, also winning two European Championships in 2008 and 2012, and made more than 700 appearances for Real Madrid.
Twitter broke out in concern as news of Iker Casillas's heart attack spread.
Spain manager Vicente del Bosque confirmed his intention to step down after the defending champions were knocked out of Euro 2016 in the Round of 16 by Italy.
Live streaming of Spain vs Croatia Group D Euro 2016 match will be available on all digital platforms like web and mobile. Croatia need a draw to qualify for pre-quarterfinals. Spain have already made the last-16. Catch live action through NDTV live blog too
David De Gea has strongly denied allegations that he organised a party at which two women were forced to have sex with two footballers
Iker Casillas made his 166th appearance for his country as Spain drew 0-0 away to Romania in an international friendly.
Raul Gudino, 19, who normally plays as a starter in the reserve team in the Portuguese second division, called Iker Casillas a great teammate and a great friend, adding that he is trying to learn everything from him to improve his skills.
The former Real Madrid goalkeeper Iker Casillas will become a father for the second time in the spring of 2016.
Iker Casillas joined FC Porto from Real Madrid in July this year.
According to reports, Iker Casillas' signing has made about about half a million euros while the total shirt sales have generated revenues of four million euros.
Jose Mourinho will aim to turn Chelsea's fortunes around in the Champions League after their continued struggles in the EPL.
Real Madrid president Florentino Perez has admitted the Spanish club was wrong in dealing with the farewell of veteran goalkeeper Iker Casillas.
Iker Casillas said he was "very excited" by the reception he has been given in Portugal and that "the affection of the fans is the biggest prize an athlete can achieve."
Iker Casillas brought to an end a 25-year period at Real Madrid last week when he departed to join Porto.
Iker Casillas announced his decision to leave for Portuguese side FC Porto after 25 years with his boyhood club in a tearful solitary press conference on Sunday
Real Madrid President Florentino Perez rubbished the reports of club captain Iker Casillas being pushed out.
Real Madrid confirmed on Saturday that a deal has been agreed that will see the custodian bring an end to his 25 years with the La Liga giants and move to the Portuguese side. The transfer brings to an end what has been a troublesome couple of years for the 2010 World Cup-winning goalkeeper -- and the 34-year-old's parents blame the club chief.
A World Cup winner and two-time European champion with Spain, Iker Casillas had clinched five Spanish titles, three Champions League trophies and two King's Cup crowns since making his first-team debut with Real Madrid in 1999.