Chile are hoping star midfielder Arturo Vidal is fit and able to play when they square off against Australia in Cuiaba on Friday.
The Juventus player has been struggling with inflammation in his right knee following an operation on his meniscus last month and has had a big question mark over his availability for the World Cup Group B games ever since.
Vidal, a free-kick specialist, has trained with the team since Wednesday and featured for 15 minutes in a 2-0 friendly win over Northern Ireland last week.
"Arturo trained like the rest of us," Chile midfielder Gary Medel said. "He did a good job and didn't have any pain in his knee.
"We hope that he can be with us for the first game.
"It will depend on him and how he feels.
"We want him to take care of himself and if he does play, we hope it (meniscus) doesn't affect him."
Chile coach Jorge Sampaoli will have two other big tests coming up with reigning champions Spain and Holland also in the pool.
Medel, who was Cardiff City's record signing when he joined them last summer, says the atmosphere in the squad is fantastic.
"We want to go as far as possible," he said. "We want to make history with this group.
"We hope to go all the way.
"We have a great generation of players and we have worked really hard to be here.
"We hope that people enjoy our play and above all, we want to be champions."
Barcelona striker Alexis Sanchez is expected to lead Chile's attack alongside Eduardo Vargas.
Group B underdogs Australia, who are coached by Ange Postecoglou, have never beaten Chile in four previous encounters.
"Chile's aspirations are not just to get out of the group but really do something in the tournament," Postecoglou said. "They have a great belief.
"Any team you face at any level who have a great deal of belief in themselves are a difficult opponent.
"You know that no matter how the game goes, they're going to stick to their way of football.
"That gives them tremendous confidence going into every game, and that's our challenge.
"That's the biggest thing for us to overcome - we're going to get tested, we're playing against the best in the world.
"Hopefully our players have a similar belief."
The biggest challenge for Australia, who are competing in their third straight World Cup finals, is the lack of experience for many of their players.
A total of seven players in the squad are currently on the books of A-League clubs.
"For a lot of these players it's their first go at the big stage and I'm sure there's a little bit of uncertainty in their heads," Postecoglou said. "If we can get through those initial moments we'll be fine."
Experienced striker Tim Cahill will lead the Socceroos' attack while veteran midfielder Mark Bresciano is doubtful with a back injury.
Crystal Palace midfielder Mile Jedinak will captain Australia.