The 34 year-old former La Liga star is off contract at the end of the season.
But he is focusing instead on ensuring Glory are part of the 2016/17 Finals Series.
Ahead of his 50th game in the competition against Brisbane Roar on Saturday night, the Spaniard spoke of his gratitude to his club and its fans.
"This experience has been wonderful for me and my family," said Castro.
"My focus now is not on the future.
"My focus is this season and to win this season and produce the best outcomes for the whole team.
"The focus now is to be part of the finals," he said.
THE FINALS … AND BEYOND
Glory need to win at least one of their remaining two matches against Brisbane Roar and Melbourne City to ensure their place in the top six.
Beyond that, the reigning Johnny Warren medallist said anything is possible.
"First we need to reach the [finals].
"If we reach the [finals], we will fight to win.
"I am here to win for Perth Glory,” he said.