The Liverpool forward had an operation on his right knee last month, and after a medical check up with the national team on Monday was included in Spain coach Vicente del Bosque's preliminary 30-man squad.
"At the moment, we cannot say if Fernando will be ready in time for the first game of the finals, but we are optimistic," Spain doctor Juan Jose Garcia Cota was quoted as saying in the local media on Wednesday.
"He has started to work outside and is still doing gym work to improve the muscle tone around the operated knee.
"He will be here (in Vigo, north-west Spain) until the squad meet up for the World Cup finals."
Torres, who scored Spain's winner against Germany in the Euro 2008 final, forms half of a lethal attacking partnership with Valencia's David Villa.
Spain kick off against Switzerland in Durban on June 16 and go on to play Honduras and then Chile in Group H.
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