Former Real Madrid and Spain star Casillas was rushed to hospital after collapsing in a training session on May 1.
The 38-year-old was discharged five days later, and he acknowledged at the time that he was unsure what the future held.
Reports later claimed Casillas had decided to retire, though those suggestions were denied by the player.
While Casillas will not be a part of Porto's first-team squad heading into next season, the goalkeeper has not officially called time on his career and will instead take up a role helping to manage relations between the players, coaching staff and directors at Estadio do Dragao for the time being.
"I'm going to do something different than I usually did, which was to be on the pitch," Casillas told Porto's TV channel.
"I'll try to make the connection between the team and the club. The coach talked to me last season when my situation happened, and he told me that he wanted me to stay with them, close to the players, near the younger players, because there would be a lot of changes."