Luiz da Silva's ruling Workers' Party said Ricardo Berzoini, the party's president, had resigned as Silva's campaign manager on Wednesday and will be replaced by Marco Aurelio Garcia.
The resignation came shortly after Brazil's electoral tribunal opened an investigation to determine if Silva was involved in a reported plot to sell documents incriminating Jose Serra of the opposition Social Democratic Party.
The scandal surfaced over the weekend, after federal police arrested an attorney who allegedly was hired by Workers' Party leaders to purchase the documents.
Serra, who lost to Silva in 2002 presidential elections, is running for the governor's seat in the leading industrial state of Sao Paulo against Workers' Party candidate Aloizio Mercadante.
According to the federal police investigation a Workers' Party aide, said he met with journalists to sell a dossier containing damaging information on Jose Serra, for 1.7 million reals ($781,000).
Bargas said Berzoini knew of the meeting with the reporters but not of the contents of the dossier.
"If there is need for a change in the campaign there is no problem" he said.
"This is a position of confidence and I am at the president's full disposal."
The tribunal's press office said the investigation will not be finished before the October 1 election.
However, if the president wins re-election and the tribunal rules against him, federal prosecutors could launch legal proceedings that could result in Silva losing his mandate.
The runner-up would then become Brazil's next president, the tribunal's press office said.