The Copa America champions start their bid to qualify for Qatar 2022 on Friday in Sao Paulo but could be without the Paris Saint-Germain striker.
“It’s a health problem that’s not entirely resolved,” said coach Tite.
The 28-year-old’s back injury flared up before training on Wednesday.
“He’s a little bit better today than yesterday,” said team doctor Rodrigo Lasmar. “We’ll see tomorrow how he responds.”
Should Neymar be forced to miss the match, Tite said he would be replaced by Flamengo’s attacking midfielder Everton Ribeiro.
Neymar’s injury travails kept him out of most of Brazil’s matches last year.
He played in only four out of 16 games and was injured in two of those — against Qatar in June and Nigeria in October.
The injury against Qatar forced him to miss the Copa America that Brazil won on home soil.
Tite said Real Madrid midfielder Casemiro would captain the side with Aston Villa’s Douglas Luiz lining up alongside him in midfield.
