Riding a wave of five straight wins, Spain have lit up the tournament, scoring 11 goals on the way to the semi-final.
France have reached the same point despite lacking attacking fluency and are yet to score from open play. France's three strikes have come from one penalty and two own goals.
Mbappe and fellow forward Antoine Griezmann have come under fire for failing to perform, but De La Fuente remained wary, particularly of the French captain.
"These kinds of footballers are unpredictable. You never know where they will appear and they never disappear completely," he said.
"His (Mbappe's) level could be slightly lower than his usual level, but 50 per cent of Kylian Mbappe could be 100 per cent of any other player.
"A player like this can decide a game at any moment. He's a genius, a world-class player, of which France have many."
Despite lavishing praise on the French captain, de la Fuente backed his own troops.
"Mbappe is a one of a kind and is exceptional," the coach said, but added: "To me, my footballers are the best."
"Knowing their potential, we will try to minimise their virtues.
"I trust we will be able to counteract them. I have blind faith in my team and know we are ready to win tomorrow."
Spain midfielder Rodri said he was not tuning in to criticisms of the French forward, considered by many to be the best player in the world.
"I don't trust what people say. I know the player he is. He can hurt any team at any time and we will have to be aware of what he does," he said.
Rodri also pushed back at suggestions France had reached the semi-final on the basis of boring football.
"Some might think they are boring but I don't see football in that way," the Manchester City midfielder told reporters.
"They're in the semi-finals and others are not. But we just want to win and play our football - and not look too much at what they do."
