Costa, who withdrew from the squad last month for personal reasons, came off injured during Atletico's 3-1 win over Club Bruges in the Champions League on Wednesday, though Atletico have yet to announce details of the injury.
Spain coach Enrique declined to say whether or not the striker had been in his plans before he was injured against Bruges.
"I don't know why people are so interested in knowing this. He got injured and that is it," Enrique told a news conference.
Spain play Wales in a Cardiff friendly next Thursday before hosting England in a UEFA Nations League tie at Real Betis's Benito Villamarin Stadium the following Sunday.
Enrique's team is top of the Nations League A Group 4 standings on six points after beating England 2-1 and hammering Croatia 6-0 last month.
"The friendly with Wales will allow us to try things out. The vital game is against England. There will be little room for experiments because we have to win," Enrique said.
The coach has also handed a first call-up to Wolverhampton Wanderers defender Jonny Castro and recalled Real Betis defender Marc Bartra and Borussia Dortmund forward Paco Alcacer, having worked with the latter pair while at Barcelona.
Barca defender Jordi Alba, however, continues to be overlooked despite showing strong form for his club.
Real Madrid pair Isco and Dani Carvajal, along with Barca's Sergi Roberto and Athletic Bilbao's Inigo Martinez, were part of the last squad but all miss out through injury.
Squad:
Goalkeepers: David de Gea, Kepa Arrizabalaga, Pau Lopez.
Defenders: Cesar Azpilicueta, Raul Albiol, Nacho Fernandez, Sergio Ramos, Marc Bartra, Jonny Castro, Marcos Alonso, Jose Gaya.
Midfielders: Sergio Busquets, Rodri, Koke, Saul Niguez, Thiago Alcantara, Dani Ceballos.
Forwards: Marco Asensio, Iago Aspas, Alvaro Morata, Suso, Rodrigo Moreno, Paco Alcacer.
(Reporting by Richard Martin; Editing by John O'Brien and David Goodman)
