Former Constitution Party leader Mohamed ElBaradei expressed his grief over the stabbing of party spokesman Khaled Dawoud on Friday.
Dawoud, a former spokesman for the anti-Morsi opposition bloc the National Salvation Front, was stabbed in his chest and hand on Friday in central Cairo.
Shortly after the assault, Dawoud told Al-Ahram Arabic news website that he was attacked by protesters while driving his car down Qasr Al-Aini Street in front of Abou Al-Rish Bridge.
He told Al-Ahram that his car was attacked and protesters pulled him out of the vehicle, beat him and stabbed him with a knife.
"The barbaric assault on Khaled Dawoud ... reflects the size of the tragedy we're living," said former vice-president ElBaradei via Twitter, adding that he wished Dawoud a speedy recovery.
Dawoud, a staunch opponent of Mohamed Morsi and the Muslim Brotherhood, resigned from the NSF in mid-August to protest the group's support for the violent dispersal of two large protest camps established by supporters of ousted president Mohamed Morsi.
The dispersal by the security forces left hundreds of protesters dead.
The liberal Constitution Party for their part accused Muslim Brotherhood protesters, who were present in Qasr Al-Aini after a failed attempt to enter Tahrir Square, of being behind the assault.