Thuli Madonsela, whose term as public protector expires in October, was quoted as saying her office was bound by law to look into a complaint lodged by the DA.
But the watchdog's budget has been cut since an investigation into a R250-million state-funded security upgrade to Zuma's private Nkandla residence.
"We want to ask the Treasury for a special fund for our special investigations. Then we can appoint a team of external forensic investigators and conclude the investigation quicker," Madonsela was quoted as saying.
Zuma is facing calls for his resignation after Deputy Finance Minister Mcebisi Jonas said last week he had been offered his boss's job by the Gupta family in November.
Other senior officials have also accused the Gupta family of wielding undue influence in government activities. The Guptas say they are pawns in a plot to oust Zuma.
Zuma got the backing of his party at a summit at the weekend.
Madonsela's office did not immediately respond to calls for comment.
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