Judge Ashraf Nafea has become the third judge to withdraw from a libel case brought by former PM Ahmed Shafiq against Wasat Party leader Essam Sultan.
Nafea cited 'conflict of interest' for his decision.
Shafiq says Sultan falsely accused him of corruption and of illegally transferring money to president Hosni Mubarak and a number of businessmen during the early days of the January 25 Revolution, in comments made via Facebook and on television.
In April, a criminal court acquitted Shafiq on charges of embezzlement and squandering public funds while serving as civil aviation minister.
Shafiq, who came in second in the 2012 presidential candidate, was civil aviation minister from 2002 to 2011 and was appointed prime minister by former president Hosni Mubarak during the January 25 Revolution.