“Casillas still has a year left on his contract and we want him to remain part of FC Porto’s structure, and not only for one year,” club president Jorge Nuno Pinto da Costa told Thursday’s sports daily O Jogo.
“Casillas is one of us and he will always have a place at FC Porto.”
The former Real Madrid and Spain star, who will celebrate his 38th birthday on Monday, was taken to hosital and had surgery on May 1 after collapsing during training.
He left hospital after five days and said he was “lucky” to be alive but had no immediate plans for the future.
“The important thing is to be here… I don’t know what the future may bring,” he said.
Casillas has 167 Spain caps, winning the 2010 World Cup and two European Championships, and also played more than 700 games for Real Madrid.
He joined FC Porto in 2015 and recently extended his contract to 2020 with the option of an additional 12 months.
He said Porto had told him they wanted to keep him until he turned 40.