The Real Madrid legend underwent surgery on Thursday after collapsing in training.
"I'm really grateful, I've been very lucky," Casillas told reporters. "I've been made to feel really loved by everyone who has shown their concern.
"I'd like to say thank you for all the support I've received on social media. I feel a lot better [...]. Thousands and thousands of people have sent me messages."
On his playing future, Casillas added: "I don't know what the future holds.
"What's most important is that I'm here."
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