The Brazilian-born forward is set to play for Vicente del Bosque's side after impressing with his form for Atletico Madrid.
The Brazil-born striker, who initially signed for the Rojiblancos in 2007, has been granted Spanish citizenship, which entitles him to switch to La Roja. Although he played in two friendlies for Brazil earlier this year, Costa never represented the Selecao in an official 'A' competition, so he is eligible to play for Spain.
Spain coach Vicente Del Bosque recently encouraged Costa to make the switch, and, according to the Spanish Football Federation [RFEF] Costa has verbally agreed to link up with the world champion for future internationals.
The 24-year-old Costa will not be eligible for selection for the country's upcoming World Cup qualifiers with Belarus and Georgia, though, due to paperwork not being complete.
"Diego Costa wants to play for the Spanish national team, although bureaucracy inhibits this for the moment," the RFER said in a statement. "Atletico Madrid player Diego Costa cannot be selected tomorrow by manager Vicente del Bosque for the upcoming games against Belarus and Georgia as FIFA have demanded additional paperwork, which is already being undertaken, even though the player has verbally expressed to the Spanish coach his desire to play for his national team in the future."
Costa has scored eight goals in seven La Liga games this season, tying Lionel Messi for the league lead and filling the void left behind by the departed Radamel Falcao at Atletico Madrid.