The Real Madrid star, who missed a penalty and was booked during the group clash, stormed off the park without addressing his teammates at full time, but Santos has insisted that the forward had a right to be angry.
"I understand, it's normal," Sky Sports News quotes the national team coach as saying.
"The best players in the world face that when there isn't an opportunity to really make it happen. That hurts a lot, more to them than to the other players.
"They always want to win, they want to be the best and they refuse to fail - and when they fail they get very upset."
A draw was enough to send Portugal into the knockout phase of the tournament while Iran bowed out.