“I would like to finish my career with FC Porto and go to the end of my contract,” the 37-year-old former Real Madrid goalkeeper told Portuguese broadcaster RTP.
“It would be nice to have only a few clubs in my career,” he added. “I spent a large part of my life at Real Madrid, which is the best club in history, but I came to Portugal and into a strong team like FC Porto and that makes me very happy.”
Casillas, who won a World Cup and two European titles with Spain, extended his contract in May shortly after Porto won the Portuguese title.
He will have a chance to compete again in the Champions League, a competition he won three times with Real, and in which he has made a record 178 appearances.
Porto kick off their domestic season on Saturday when they play Aves, surprise winner of the Portuguese Cup last season, in the Supercup.
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