On 4 August, Casillas started in Porto's 3–1 victory over Desportivo das Aves in the 2018 Supertaça Cândido de Oliveira. He surpassed Giggs' record during the 2018–19 season, appearing in his 20th consecutive UEFA Champions League campaign. On 11 December, Casillas, in a 3–2 away win over Galatasaray, became the first player to reach the knock-out stage 19 times, and become only the second player after Cristiano Ronaldo to win 100 Champions League matches. He made 31 league appearances throughout the season as Porto finished in second place, but his season was cut short after he suffered "an acute myocardial infarction" during training on 1 May 2019. He was discharged from hospital on 6 May, but commented that he was uncertain about his future.