Casillas was making his 108th appearance for Porto, having previously turned out 725 times with boyhood club Real Madrid while earning 167 caps for Spain.
He captained his country to their first World Cup title in 2010 as well as consecutive European Championships, in 2008 and 2012.
The 36-year-old broke through into the Real first team as a teenager in 1999, winning the Champions League on three occasions before moving to Porto in 2015.
Porto have already announced that Casillas will leave at the end of the season following a three-year stint in Portugal as the club look to trim their payroll.
Monday’s loss to Belenenses, a second defeat in three matches, left Porto a point behind defending champions and leaders Benfica with six games of the season remaining.
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