Despite relying on the striker's goals, the coach is refusing to play him against Barcelona unless he is fully fit, with Adrian Lopez ready to take his place in the second leg
The Vicente Calderon will play host the second leg of the Champions League quarter-final between La Liga's top two, with the Rojiblancos arguably holding the advantage as they held the Catalans to a 1-1 draw at Camp Nou in the opener.
Costa picked up an injury in that game and, despite being rested in the 1-0 weekend win over Villarreal, may not have recovered in time to play a part in the crucial European tie leaving Adrian Lopez to fill his boots up front for the hosts.
"Diego Costa for us is like Lionel Messi for Barcelona or Cristiano Ronaldo for Real Madrid," Simeone told reporters on Tuesday.
"If Diego Costa is fit, he plays. If he is a little less than 100 per cent, he will be on the bench. Otherwise he'll be out. We will have a look at Diego Costa in training later.
"If he doesn’t make it, Adrian Lopez will play. If Adrian plays I am sure he will play a great game for us. We have rotated some players in the last few games which is important to keep the team fresh.
"This will be a passionate game between two teams with different styles."
Atletico hold a one-point lead over Barca in La Liga's title race and, should the Spanish giants remain tussling until the end of the campaign, the final game of the season for these two teams is against each other and would be a mammoth match.