Former presidential candidate Khaled Ali was injured on Friday as he took part in protests against the Muslim Brotherhood at the Islamist group's headquarters in Cairo's Mokattam district.
Ali, a prominent leftist lawyer, sustained a shoulder injury and was hospitalised shortly afterwards. According to the Ahram Arabic news website, Ali was injured after trying to end a fight that had broken out.
He was released from hospital later in the day after receiving treatment.
Clashes erupted on Friday between Brotherhood supporters and opponents near the Muslim Brotherhood headquarters. Rocks flew between both sides in the nearby streets, with reports of injuries.
Earlier, protesters had already started gathering for 'Friday of Restoring Dignity' demonstrations at the headquarters in the hilly Cairo suburb to demonstrate against the Islamist group, while Brotherhood members and supporters formed human chains around the building to protect it from any possible attacks.