Costa, Atletico's top scorer, and playmaker Arda limped out of last weekend's La Liga title decider at Barcelona with hamstring and hip injuries respectively and there were fears they would not be available for the showpiece in Lisbon.
"Later on we will evaluate their condition and see if they can train better today," Simeone told a news conference. "We will see how they themselves are feeling and depending on what the team needs we will make a decision," added the Argentine.
"Costa and Arda are important players but they are just two names on the list. It will either be them playing or two other lads who already know who they are."
Costa and Arda trained with their team mates on Thursday before Atletico flew to the Portuguese capital from their base near Segovia on Friday morning.
They will train again later on Friday at Lisbon's Stadium of Light, which will host the first final featuring two teams from the same city in the 59-year history of the competition.
Atletico are seeking their first European Cup title and will be trying to deny Real a record-extending 10th.