Shilton is surprised by Ferdinand's actions.
He said: "Playing for your country, for me, was the ultimate but that seems to have changed a little bit.
"I don't know the circumstances of what went on but I wanted to get every cap I could. To play in the World Cup and try to win something for England was the ultimate.
"I don't know why Rio isn't playing, whether it's an injury or not, but if he has just pulled out for no reason then I totally disagree with that."