It was the first time Mubarak, 85, had missed a session in the retrial, which got underway in May. The judge adjourned proceedings until August 25.
Violence erupted across Egypt on Friday during protests by Islamist opponents of the army-backed government that took power from president Mohamed Mursi, who became the second head of state to fall in two years when the military removed him on July 3.
Mubarak is being held at Tora Prison on the southern outskirts of Cairo - the same facility where senior members of Mursi's Muslim Brotherhood have been held since they were arrested in a crackdown on the organisation.
Mubarak and Adly were convicted and sentenced to life in prison last June for failing to stop killing during the 2011 uprising that swept him from power. But a court ordered the retrial in January after accepting appeals from both the prosecution and the defence.
Each cited different shortcomings with a trial that was criticised for the weak evidence offered by the prosecution. Mursi is also being detained, but at an undisclosed location. He faces a formal investigation into accusations stemming from his escape from prison during the uprising against Mubarak. The accusations against him include conspiring with the Palestinian group Hamas and murder.