Atletico Madrid striker Costa, who announced he would represent Spain at international level in October, previously played in two friendlies under the Brazil flag in March 2013.
The 25-year-old, who was born in Brazil, was slammed by Scolari after his announcement, with the Brazil boss claiming he was 'turning his back on a dream of millions'.
And on Monday, Scolari revealed Costa - whose World Cup campaign ironically hangs in the balance due to a hamstring injury - had discussed with him representing the hosts at the 2014 tournament.
"I was going to summon him for the World Cup," Scolari said, as reported by AS.
"Was I wrong? I don't know. He would be at the World Cup with Brazil. I talked to him twice about it.
"The problem is there are other interests behind it. With Diego Costa becoming a naturalised Spaniard, another space (at Atletico) opened up in Europe.
"There's a whole set of interests. Diego Costa would be with us. He plays as a seven, a nine, or even as an 11. People to try to run him over and go crashing. He's strong as a bull."
Costa has made one appearance for Spain, playing 90 minutes in their 1-0 win over Italy in March.
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