The Atletico Madrid striker has been hampered with hamstring trouble in recent weeks – an injury that saw him substituted after just nine minutes during last month’s Champions League final defeat to Real Madrid.
Despite concerns over Costa’s fitness, the 25-year-old managed to play 73 minutes in Spain’s 2-0 win over El Salvador on Saturday – his first appearance since Atletico’s 4-1 defeat to their arch rivals on May 24.
While declaring himself fit for the World Cup, the Chelsea-bound striker says he is pleased by the reception he’s received from Brazil fans despite turning down the opportunity to play for Luiz Felipe Scolari’s side.
“Things are going well for me,” Costa said. “People have treated me well and in the manner I hoped. I have the support of most people who understand what has gone on.
“My parents are very happy that I am here, close to them. They support my decision.
“I needed the match with El Salvador. Now I am fine and I will have no problems for the first match.”
Spain, who will be competing in Group B, will face Chile on 18 June and Australia on 23 June.