Costa Rica coach Jorge Luis Pinto is worried Arjen Robben will try to give Holland an advantage by diving in Saturday night's World Cup quarter-final in Salvador.
Robben was accused of diving to win a penalty in Holland's second-round match against Mexico.
The winger denied the accusation but did admit to exaggerating a fall earlier in the match.
And that has Pinto concerned ahead of Saturday night's last-eight meeting.
"This is one of the most important questions I have been asked in this World Cup," Pinto said.
"Diving. This is something that makes us worry a lot. We're really worried about that.
"I would like to ask FIFA and the referees to watch Robben closely. We're really worried about his diving.
"He has admitted to doing it," Pinto added. "I hope the referee watches him very closely tomorrow.
"I would like FIFA and the referee to watch out because it is very important and can have a huge influence on the result."
Ravshan Irmatov of Uzbekistan will be taking charge of the match and Pinto hopes he is brave to book Robben should he dive.
"That may be the most logical solution," he said. "Maybe he would have to leave the field because he gets two yellow cards for diving.
"Why not? That could happen. I want to trust the referees. Let's see what happens."
Costa Rica are big underdogs against the Dutch, who have been one of the most consistent teams in Brazil.
Belgium will also be looking to upset the odds when they take on Argentina in Saturday's other quarter-final in Brasilia.
Argentina may have some of the best attacking players on the planet, but Belgium have vowed to go on the attack.
"We have studied the opposition and we will not change our philosophy," Belgium coach Marc Wilmots told a press conference in Brasilia on the eve of the game.
"We will not just defend. We will go forwards. We can make history and the players realise that."
The only other time that Belgium made it through to the last four was in 1986 when Diego Maradona's brace sent the Red Devils home from Mexico.
This time around the Argentinians have won all their matches, but only by a single goal.
That has not impressed Maradona, who managed Argentina before Sabella's predecessor Sergio Batista.
''It seems to me that Argentina today has no idea,'' the 1986 World Cup-winner told Spanish newspaper AS.
''In the first half against Switzerland the team did not have one chance.
''My team were a lot more offensive than this one.
''It looks bleak for us if I'm honest. I wish the team played differently, that it exploited all the ability its players have.
''We haven't seen the best from them, neither tactically nor individually, and this worries me."