Around 50 leading members of Tamarod (Rebel) have issued a statement backing Hamdeen Sabbahi for president.
The move comes a day after the group suspended three senior members—Hassan Shahin, Mohamed Abdel-Aziz and Khaled El-Kady—for announcing their support for the Nasserist politician's candidacy.
Tamarod—which led the campaign against Islamist president Mohamed Morsi—officially backs army chief Abdel-Fattah El-Sisi for president – although he is yet to declare he will stand.
Tamarod does not belong to one particular member or current, the statement said. It belongs to all those who collected signatures against Morsi and protested for his ouster.
It was created by young people with diverse political views who united to achieve the revolution's goals of bread, freedom and social justice, the statement added.
They said they back Sabbahi because he rejects Mubarak's corruption and Morsi's terrorism and has a vision to fulfil the goals of the January 25 and June 30 revolutions.
Sabbahi—who leads the Popular Current and came third in the 2012 election—announced his candidacy on Saturday.
Tamarod's Qalioubiya chapter will also be supporting Sabbahi and rejects the expulsion of members for opposing El-Sisi's candidacy, its coordinator Khaled Saad said on Sunday.
All Tamarod members in Qalioubiya oppose a presidential bid by El-Sisi, Saad told Al-Ahram Arabic news website, because it would allow people to describe what happened on 30 June as a coup.
Some Tamarod members are calling for a breakaway group because founder Mahmoud Badr insists on supporting El-Sisi and takes harsh action against those who oppose him, Saad said.
Saad added that he was communicating with expelled members Shahin and Abdul-Aziz about launching a new group called Revolutionary Tamarod.