Coach Mano Menezes said Saturday that Brazil had much to fix before facing Belarus in Manchester on Sunday.
Brazil, he said, had too many tactical and individual mistakes in the 3-2 win over Egypt, when it nearly relinquished a three-goal first-half lead.
"We made errors when trying to keep the ball in the attack and made errors with the positioning in the back," he said. "We will have to work to fix that before we play our next match."
Brazil is trying to win its first gold in football. The team is one of the main favourites because it brought many of its top players to the competition.
The Brazilians scored three goals in the first 30 minutes against Egypt and appeared in control of the match at the Millennium Stadium. But Egypt made it interesting after a goal off a corner in the 52nd and another following miscommunication between Brazilian defenders in the 76th.
Real Madrid left back Marcelo headed a ball backward in the play that led to the second goal and Inter Milan defender Juan failed to clear the ball as it bounced inside the area.
Brazil was able to keep possession after the goals and held on, but players know they can't afford the same risks in the match against Belarus.
"We can't let those mistakes happen again," striker Neymar said. "I'm sure that in this next match it will be different and we will be able to get another win."
Menezes said that against Belarus, his players will have to do a better job keeping position and covering for their teammates when Brazil loses possession up front, a problem that he said allowed Egypt to threaten in the opener.
The coach had only two days in between matches to try to make the changes, though. On Saturday he spent a lot of time talking to the players in the final practice before the game and then the team had a light training session.
"There is no time to practice properly so we will try to make the adjustments with a lot of talking, but I'm confident that we will improve in this next match."
Brazil is expected to start with the same 11 from the opener, with Neymar, Leandro Damiao, Oscar and Hulk playing forward and Alexandre Pato on the bench again.
The Olympic tournament is played with under-23 teams but each nation can use three overage players. There are high expectations in Brazil because many of the team's top players are under 23 and the squad playing in the Olympics is likely to be similar to the one which will try to give the nation the World Cup title at home in 2014.
Brazil earned silver medals in 1984 and 1988, and bronze in 1996 and 2008.
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