In July 2019, following his heart attack two months earlier, Casillas returned for pre-season training. Later that month, Porto announced that he had been given a role with the club's coaching staff as he continued his recovery. In August, he was named in Porto's squad for the 2019–20 season. In September, he shared the results of his medical tests on social media; at the end of the month, he stated that he would wait until March of the following year to see how he is progressing with his recovery before deciding whether to return to playing or retire. In October, he posted a photo of himself working out in the club's gym on Instagram. He resumed training on 4 November.