Casillas has not played since suffering a heart attack in May last year.
The 39-year-old then played for Porto. During his time at Real Madrid, he won the league five times and the Champions League three times in over 700 matches for the club. With Spain, he won the World Cup gold in 2010 and the European Championship gold in 2008 and 2012.
He played 167 international matches. The very first he did as a 19-year-old against Sweden at Ullevi 2000 in a training international match before the European Championship finals.