- Ronaldo thinks Brazil will make changes
- Duarte: Thiago tears talk of the town
The former Selecao midfielder told French radio station RMC that "luck has gone with us" after a penalty shootout win over Chile put the hosts in the quarterfinals.
And as they prepare to take on Colombia in the last eight, former Lyon player Juninho, 39, said: "We're all worried.
"A year ago, Brazil won the Confederations Cup final against Spain. The coach decided a year before the World Cup that he already had his team, that he had 11 players and it was that team he would line up at the World Cup.
"Right now, there are quite a few players who are out of form, such as Dani Alves on the right or Fred up front.
"Paulinho went to Tottenham, but he didn't play. The first half of Oscar's season was satisfactory with Chelsea, but he ended it in difficulty.
"With the Brazil team, you can't decide the 11 players that are going to play the World Cup a year before it starts. He hasn't worked or thought of another solution."
Juninho claimed Brazil's players "feel that their team is going through a difficult patch" after the Chile victory produced some strong criticism in the Brazilian media.
He warned that Colombia and James Rodriguez, who has been one of the stars of the World Cup so far, would pose a tough challenge -- but added that their attacking approach could end up helping Brazil.
"They'll perhaps be the first opponents who are going to attack Brazil," he said. "And that is dangerous for Colombia, too."
Scolari: We have the skills to get to the finals
Brazil coach Luiz Felipe Scolari explains the difficulties his team face as they advance deeper into the tournament.
Silva: Colombia is no different from our team
Brazil coach Luiz Felipe Scolari and captian Thiago Silva comment on the respect they carry for Colombia and the similarities between both groups.