Morata started the campaign alongside record signing Joao Felix when Costa was sidelined by an adductor injury.
After Morata succumbed to a knee problem, Simeone then opted to field Costa with Joao Felix in Atleti's attack.
With Morata fully fit and Atletico having failed to score in successive La Liga games against Real Sociedad and Celta Vigo, Simeone could select the trio together for Wednesday's trip to Real Mallorca.
"As I always said, and I said it before in some other press conferences, when Alvaro and Diego are both strong and in shape it's very likely that they will play together," he told reporters.
"They have physical strength, increase our chances of scoring goals and open the possibility of other players coming in to play just behind them.
"Alvaro is back and Diego has played already a few times, we hope they can stay in good shape so they can play together.
"Alvaro has always been related with goals, he's a great reference in the area. [A lack of goals] wears down strikers a lot, so if Costa plays alongside him we will have opportunities to generate or attempt danger.
"And if it's Joao or [Angel] Correa playing behind them we will try to share the efforts during the 90 minutes tomorrow."
Costa has only scored once in competitive action this year but Simeone again backed the Brazil-born Spain international to recover the form that fired Atleti to La Liga glory in 2013-14, when he hit 27 top-flight goals.
"It's true that not getting frequent chances to score is worrisome for a striker," Simeone said. "We work alongside Diego, listening to what he sees and feels and telling him what we think he has to improve.
"And as I said after the last game he has a great challenge to face individually, of course he helps the team a lot, but individually he has to rebel against a situation that's not usual for him."