Casillas suffered the attack while training for Porto's upcoming match against Aves.
Porto goalkeeper Iker Casillas suffered a heart attack while training, the club confirmed Wednesday.
The 37-year-old was taken to the hospital and is now in stable condition. The club told Portuguese news channel TVI24 that Casillas underwent surgery for an acute myocardial infarction and is not expected to return for Porto in the Primeira Liga this season.
Casillas began his soccer career in Real Madrid's youth system in 1990 and was promoted to the senior team in 1999. He remained with the club for 16 seasons until departing in 2015 to join Porto. While making 725 appearances for Real Madrid–the second most in club history–Casillas won five La Liga titles, two Copa del Rey titles, four Supercopa de Espana titles, three UEFA Champions League titles, among other accomplishments. He also won the World Cup with Spain in 2010.
Real Madrid released a statement of support for its former captain, saying: "Real Madrid C. F. wishes to offer its full support to our beloved captain Iker Casillas. Iker Casillas has shown us how to overcome the most incredible challenges throughout his professional career, adding significantly to our club's successes. He's shown us that giving up has no place in our way of life and demonstrated time and again that staying strong during the hardest of challenges is the only path to victory. Real Madrid C. F. and all of madridismo look forward to seeing our legendary captain back in good health as soon as possible and we send him all the encouragement in the world."
Casillas himself shared a message from his hospital bed, indicating that the worst was over and that he was on the road to recovery.
Sergio Ramos, a longtime Spain and Real Madrid teammate of Casillas, was among the first to publicly react to the news, with support pouring in from all around the soccer world soon after.
Spanish tennis player Rafael Nadal also wished Casillas well.
Whether Casillas plays again remains to be seen, with his career clearly second to a clean bill of health going forward.