Brazil's troubled build-up to football's Copa America hit another snag Thursday when midfielder Luiz Gustavo became the sixth player to withdraw from the squad, citing "personal problems."

It comes a day after veteran striker Kaka pulled out with a hamstring injury before Brazil open their Copa America Centenario campaign against Ecuador in California on Saturday.

Wallace of the Brazilian side Gremio has replaced Luiz Gustavo.

"In a discussion with the technical staff of the Brazilian team, the Wolfsburg player has asked to be released from the squad due to personal problems," the Brazilian Confederation said in a statement, without giving more details.

Kaka had been an injury replacement for Bayern Munich's Douglas Costa.

Other players ruled out because of injury include Ricardo Oliveira Santos, replaced by Jonas, goalkeeper Ederson and Barcelona midfielder Rafinha.