Athletic Bilbao's 35-year-old striker Aritz Aduriz, who has hit a rich vein of form late in his career, was named on Friday in coach Vicente del Bosque's 25-man selection instead of Costa, who has failed to recover from a hip problem.
Del Bosque said Costa suffered the injury as Chelsea were knocked out of the Champions League by Paris St Germain on March 9, before the striker played again against Everton in the FA Cup three days later.
"Against PSG he felt some discomfort, after four days he played and has not fully recovered yet," Del Bosque said on Friday. "This is why we've chosen not to include him this time."
Costa, who has scored just once for Spain in 10 appearances, was sent off in Chelsea's 2-0 defeat to Everton on Saturday, but has hit a purple patch of form for his club since former manager Jose Mourinho was sacked in December.
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His replacement for Spain, Aduriz, has also been in good goalscoring form this season and is the top-scoring Spaniard in La Liga with 17, while also heading the Europa League scoring chart with eight.
Aduriz, who won one previous Spain cap in 2010, came through the Athletic youth ranks, but developed a reputation as a journeyman after playing for several clubs before returning to Bilbao in 2012.
"He's a forward we've always liked, he scores, he brings about a great deal of confidence and that's great for us," Del Bosque said.
Spain visit Italy on March 24 and Romania three days later.
Squad:
Goalkeepers: Iker Casillas, David De Gea, Segio Rico
Defenders: Juanfran, Mario Gaspar, Gerard Pique, Marc Bartra, Jordi Alba, Sergio Ramos, Nacho Fernandez, Cesar Azpilicueta
Midfielders: Cesc Fabregas Sergio Busquets, Mikel San Jose, Sergi Roberto, Koke, Thiago Alcantara, Isco
Forwards: David Silva, Juan Mata, Paco Alcacer, Alvaro Morata, Aritz Aduriz, Nolito, Pedro Rodriguez
(Reporting by Toby Davis,; editing by Pritha Sarkar)
