Costa has not appeared since limping off in Atletico Madrid's UEFA Champions League final defeat to city rivals Real Madrid last month.
The Brazilian-born forward has been battling muscle problems in recent months, but Spain coach Vicente del Bosque will be hoping the 25-year-old will be fit enough to give his side an extra attacking dimension as they seek to defend their World Cup title.
And while a start in Spain's World Cup opener against the side they beat in the 2010 World Cup final - the Netherlands - may be unlikely, Costa could see some game time this weekend as he looks for match sharpness.
Club-mate Juanfran - who has an injury problem of his own in the form of a troublesome ankle - has tipped the striker, widely linked with a switch to Chelsea, to have a big tournament.
"He (Costa) is great and I'm convinced he will be one of the great players of the World Cup," Juanfran said.
Spain have opted to play only two pre-tournament friendlies, and begun with a 2-0 win over Bolivia last Friday.
Fernando Torres scored from the penalty spot before Andres Iniesta's late goal sealed a win that was not as comprehensive as Del Bosque would have liked.
But a stronger team will be expected this time out as Del Bosque moves closer to picking his XI for the Netherlands clash.
The former Real Madrid boss will be wary of a slow start at the World Cup, with Spain stunningly shocked by Switzerland in their first game of the 2010 event.
As history shows, they recovered superbly to be crowned World Cup winners for the first time, but another first-up defeat could be costly in a tough Group B that also contains Chile and Australia.
And while Australia - the lowest-ranked team at the World Cup in 62nd - should not present much of a test to Spain, Chile are sure to enjoy the familiar South American surroundings.
However, El Salvador, ranked 68th in the world, are unlikely to present any real challenge to Spain.
They have won just one of their last eight matches - a slender 1-0 triumph against Haiti at the CONCACAF Gold Cup - but were valiant in defeat against the Ivory Coast on Wednesday.
Arturo Alvarez's late penalty ensured they only lost 2-1, but Spain should present a much sterner test in Maryland, US.
