A South African court has dismissed former President Jacob Zuma's attempt to remove the prosecutor from his upcoming corruption trial.

Zuma’s lawyers sought to appeal an earlier ruling that rejected his effort to have the prosecutor taken off his corruption case. That application was dismissed Wednesday by Pietermaritzburg High Court Judge Piet Koen, on the grounds that Zuma’s attempt to remove the prosecutor “lacks reasonable prospects of success.”

Zuma, South Africa's president from 2009 to 2018 before he was ousted by his African National Congress party amid wide-ranging allegations of corruption, had argued that lead prosecutor Billy Downer is biased against him. His lawyers accused Downer of leaking confidential information about his case to the media and being a witness in a separate case against him by the opposition party, the Democratic Alliance.

The efforts to have Downer removed have delayed the start of Zuma’s corruption trial, which is now scheduled to begin on April 11.

Zuma is accused of receiving bribes from French arms manufacturer Thales through his former financial adviser Schabir Shaik, who was convicted and sentenced on related charges in 2005. Downer led the prosecution that resulted in Shaik’s conviction.

Zuma's lawyers still have the option to petition the country’s Supreme Court of Appeal, which could further delay the corruption trial.

In a separate case, Zuma was sentenced to 15 months imprisonment for defying a Constitutional Court order that he testify at a state-backed commission of inquiry investigating corruption allegations during his presidential term.

Zuma's imprisonment last year sparked riots in South Africa's KwaZulu-Natal and Gauteng provinces in which more than 300 died and an estimated $1.7 billion damage to property that was looted or destroyed.

Zuma was released from prison in September on medical parole, for an undisclosed ailment. In December the courts ruled that Zuma's parole was invalid and ordered him to return to prison, a decision that his lawyers are appealing.