(CNN)Former Spain and Real Madrid goalkeeper Iker Casillas says he "does not know what the future will be" after suffering a heart attack earlier this month.
The 37-year-old Casillas was taking part in training with current club Porto when he suffered an acute myocardial infarction, which occurs when a part of the heart doesn't receive enough blood.
Speaking to reporters from outside the hospital in Porto after being discharged on Monday, Casillas paid tribute to the medical staff that had cared for him over the past week, and expressed his gratitude for the messages of support.
But he also stressed that he would take his time over making a decision about whether to return to football in the future.
"I will have to wait a couple of weeks or a couple of months, the truth is I don't care (how long)," Casillas said.
"I don't know what will happen in the future but the most important thing is to be here and to be able to speak with calm."