This year's hosts had no problem finding the net in their only warm-up game so far, putting four past Panama on Tuesday in a display where they were rarely required to get out of first gear.
Neymar, Dani Alves, Hulk and Willian were all on target in Goiania as Brazil kicked off their preparations with a comfortable victory.
However, Scolari still voiced his concern at aspects of the performance, having previously been critical of the squad in recent training sessions.
The experienced coach revealed their training had been "all wrong" and the win over Panama failed to ease his worries completely ahead of their tournament opener against Croatia on June 12.
That said, the man who guided Brazil to the World Cup in 2002 insisted he felt more confident after Tuesday's victory than he had done beforehand.
"I still have concerns, but not at the same level I had on Sunday," he explained.
"We did not allow our opponents the opportunity to counter-attack and that is what I need to see because our team has the quality to score one or two goals.
"If we do not allow our opponents easy counter-attacks, we have a chance to win games by even more. We improved, but we still have a long way to go."
Scolari also suggested he would look to put out his strongest team in Sao Paulo against Serbia, as he looks to create a sense of continuity ahead of their opener.
That means Neymar will likely start again, having played the full match against Panama in midweek.
The skillful Barcelona forward, who will be expected to play a leading role in Brazil's bid for World Cup glory on home soil, missed the latter stages of the Liga season with a foot injury but has expressed confidence at being ready in time for the opening game.
"I'm not (yet) ready physically," he acknowledged after the win over Panama. "I lack game time, but there's still time to improve because the first game is nine days away."
Serbia will likely pose a sterner test than Panama, with the Europeans sitting five places higher than the Central Americans in the FIFA rankings, although the two nations played out a 1-1 draw on Saturday in Illinois.
That result helped contribute to an eight-game unbeaten run for Ljubinko Drulovic's side - who will hope to continue their preparations for the UEFA Euro 2016 qualifiers with what would be a memorable victory.
After fixtures against Brazil and France, Serbia begin their quest to qualify for the European Championship with a trip to Armenia in October.
