The Portuguese club said Casillas fell ill during a practice session and remains hospitalized, but the “heart condition has been resolved.”
It said the 37-year-old Spaniard is “doing well” and is in stable condition.
Porto said the practice session at the team’s training center was interrupted so doctors could attend to Casillas.
No timeline was given for how long the goalkeeper will be sidelined. Defending champion Porto trails Benfica by two points in the Portuguese league with two games left.
Casillas joined Porto in 2015 after 16 seasons with Real Madrid, which he helped win five Spanish league titles and three Champions League trophies.
Casillas also helped Spain’s national team win one World Cup and two European Championships.
The goalkeeper’s contract with Porto was recently extended until the end of the 2019-20 season, with an option for another one-year extension.
Source: FOX Sport