The publication reported on Friday that Jorge Pinto da Costa Pinto, the president of his club FC Porto, disclosed this.
Pinto told the daily that the Portuguese club was already looking for a new goalkeeper to replace 37-year-old Casillas.
But he said he still wanted to keep the Spaniard in the club’s structure, with a yet unspecified role.
FC Porto did not respond to a request for comment.
Casillas, who joined the 2004 European champions in 2015, played 725 times for Real Madrid, winning three UEFA Champions Leagues and five La Liga titles.
For Spain, he won the FIFA World Cup in 2010.
Casillas was released from hospital on May 6 after suffering a heart attack in training.
He has said he was not sure if he would continue playing.