Rebel (Tamarod) has said it would not oppose a presidential bid by army chief Abdel-Fattah El-Sisi, just days after urging him not to run.
The group, which spearheaded mass nationwide protests against Islamist president Mohamed Morsi on 30 June, said on Monday it would not oppose "the aspirations" of people who want El-Sisi to run for president.
However, it said it would not officially back a presidential candidate until after the constitution referendum on 14-15 January.
The referendum is the first watershed in a roadmap the interim authorities say will reinstitute democracy following the ouster of Morsi by the army amid mass protests against his rule on 3 July.
The group has urged Egyptians to vote for the charter, which it labelled a "decisive and critical battle" on Egypt's path to democracy.
The referendum will be followed by parliamentary and presidential polls by mid-2014. Interim President Adly Mansour has yet to decide which poll will be held first.
Last week, Rebel counselled army chief El-Sisi, who is also defence minister, against running for the post.
"Abdel-Fattah El-Sisi should not run for the presidency in order maintain his image as a popular hero who has fulfilled his duty to the nation," the statement said.
El-Sisi has sent contradictory signals on whether he would run, by first saying he does not seek power and more recently leaving chances for a presidential bid open.
He has become enormously popular after he led the ouster of Mohamed Morsi after millions of disillusioned Egyptians protested against him.
On Monday, Rebel reiterated its calls for presidential elections to precede parliamentary polls, saying an early presidential vote was the chief demand at its inception.
Nasserist leader Hamdeen Sabbahi, who came third in last year's presidential poll, is the only politician defeated by Morsi in 2012 to declare his candidacy in the upcoming poll.