Spain coach Vicente del Bosque now appears more confident Diego Costa will make the cut when the final 23-man squad for the tournament is revealed on Saturday morning.
Costa's troublesome hamstring injury has proved a headache for Del Bosque, who fought hard last year to persuade the Brazil-born centre-forward to switch to La Roja from the country of his birth, only to see him risk the injury during Atletico Madrid's last two games of the club season.
The issue played a role in Spain postponing the naming of their travelling party for the tournament, but speaking ahead of Friday's warm-up game against Bolivia the veteran coach suggested that the last week had been useful for Costa -- and Manchester City winger Jesus Navas -- to improve their fitness ahead of the final squad.
"The outlook is good," Del Bosque said. "On Friday they will have tests. We will make the decision on Saturday morning."
With Real Madrid and Atletico Madrid players being given a week off to rest after last weekend's Champions League final, Del Bosque has a more limited pick for Friday's friendly against opponents who have not qualified for the World Cup and are ranked 71st in the world by FIFA.
The game at Sevilla's Estadio Sanchez Pizjuan -- where Spain beat England 2-0 in a friendly on their last visit in February 2009 -- was not a final test or eliminator for any players, Del Bosque said.
"Of the 19 we have, 17 will play," he said. "Nobody has to show anything. Those who are here deserve to be here, as do so many others. They have done a lot to be here."
Among all the changes Manchester United goalkeeper David de Gea and Athletic Bilbao midfielder Ander Iturraspe are likely to make their senior Spain debuts, as is 20-year-old Barcelona winger Gerard Deulofeu -- who was not named in Del Bosque's preliminary 30-man World Cup list.
Deulofeu -- who impressed last season on loan at Premier League side Everton -- will not be in the 23, but could still get a late call if a player suffers an injury setback before the tournament starts, Del Bosque suggested.
"We have brought Deulofeu on his own merits, and also as an example for other young players," he said. "We believe in him and he is in option if there is a serious injury. He is a unique player, there are few of his style, so we wanted to bring him in."