Casillas suffered a heart attack on May 1 during training with the Portuguese club and had to be rushed to hospital. When he was released five days later, he made no commitment on whether he would be able to play again professionally.
Casillas joined Porto in 2015 after helping Real Madrid win five Spanish league titles and three Champions League trophies. He also helped Spain win one World Cup and two European Championships. Casillas has a contract with Porto until the end of the 2019-20 season, with an option for another year.
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