Morocco were the first team eliminated from the World Cup group stage and will head home after the match but the North African side would love to throw a wrench into Spanish plans.
The Moroccan players will also be relaxed since they are only playing for pride making it hard for Hierro to implement a game plan against a team that may change their playbook and offer up something completely unexpected.
"Always when we play against teams that are eliminated we don't know what they are going to do," Hierro told reporters on Sunday. "We can't get into the coach's head, we don't know how they are going to play tomorrow it could be a very big surprise and we can't take anything for granted."
Spain, on four points after drawing 3-3 with Portugal and beating Iran 1-0, need a draw to guarantee their progress to the last 16 but will be looking to win and outscore Portugal, who face Iran, in case goal difference decides who finishes top.
While Morocco may be bottom of the table but they have not gone down without fight. With a little more luck and better finishing they might have been in a position to qualify for the knockout stage after two heart-breaking 1-0 losses.
"If you look at their first match (against Iran) they lost it in the 95th minute with an own goal and they had an excellent game against Portugal so you are talking about a tough nut to crack," said Hierro.
"Sometimes people might relax in a third match but we can't afford to relax, we need to be very much awake and (have) our eyes very much open. We are aware Morocco are not going to give anything away."
Hierro said he was not quite sure what kind of Morocco side he will face at Kaliningrad Stadium but whatever it is he knows the type of team he will be sending out.
"I don't think we can start second guessing or speculating about what Morocco are going to do," said Hierro. "We need to have faith and trust in ourselves.
"We shouldn't start second guessing how the opposing coach (Herve Renard) might be thinking, how Morocco are going to play it, what players are going to be in their lineup, we need to focus on our side."
(Editing by Ken Ferris)
