Casillas suffers heart attack at training

Getty Images

Casillas suddenly collapsed while training with FC Porto on Wednesday, and since the health scare Casillas has taken to Twitter to reassure his fans.

"Everything under control, a big fright but strong as ever," Casillas's tweet read. 

"Huge thanks for all the messages and love." 

The 37 year-old's heart attack prompted an outpouring of support from the football world, with some of the Spaniard's former team-mates and opponents alike sharing their well wishes on social media.

Casillas won five LaLiga titles and three UEFA Champions Leagues during 16 decorated seasons with Real Madrid, while winning UEFA Euro 2008 and Euro 2012 along with the 2010 FIFA World Cup with Spain.