Liverpool's Alisson, who has had a series of recurring injuries recently, told a press conference at Brazil's hotel in New Jersey that he was 100% fit to play in his third World Cup.
Answering a question about the status of Brazil, as other teams such as France and current champions Argentina are seen as better prepared, the 33-year-old said being among the favourites "is no guarantee for anybody" and adds pressure on the team.
"What really matters is the condition you are in at the first game. We are ready," he said, adding that the environment has been good after the problems Brazil faced during the South American qualifiers.
They qualified fifth, behind Argentina, Ecuador, Colombia and Uruguay, having appointed Italian Carlo Ancelotti as coach before the final two matches, when they won one and lost one.
"This last cycle was hard; we felt it deeply. But everything started to get better once Ancelotti arrived. He has a very strong presence in the group and gives us tranquillity to work," said Alisson.
Ancelotti has been with five-time champions Brazil for nearly a year. The first foreign head coach in the job, his results have been mixed, but many trust his leadership as key to bringing the World Cup back to the country after 24 years.
Brazil's first game will take place against Morocco on Saturday at MetLife Stadium in New Jersey.
Alisson said Ancelotti, 67, had been keen on improving the team's defence, which has frequently struggled.
"Some of those goals could have been avoided. We are working on it, because the World Cup is a short tournament. We know we will always have chances to score because of the quality of the team," he said.
Asked if he was excited to join the four Brazilian goalkeepers who have been to three or more World Cup tournaments, he said he wanted to join another group, the champions one.