ElBaradei planned a news conference later on Wednesday.
Buoyed by the massive turnout on Tuesday, the mostly secular opposition held a series of meetings late Tuesday and Wednesday to decide on next steps in the standoff that began Nov. 22 with Morsi's decrees that placed him above oversight of any kinds. It escalated after the president's allies hurriedly pushed through a draft constitution.
While calling for more mass rallies is the obvious course of action, activists said opposition leaders also were discussing whether to campaign for a "no" vote in a Dec. 15 constitutional referendum or to call for a boycott.
Brotherhood leaders have been calling on the opposition to enter a dialogue with the Islamist leader. But the opposition contends that a dialogue is pointless unless the president first rescinds his decrees and shelves the draft charter.
Vice President Mahmoud Mekki called for a dialogue between the president and the opposition to reach a "consensus" on the disputed articles of the constitution and put their agreement in writing and have it discussed by the next parliament. But he said the referendum must go ahead and that he was making his "initiative" in a personal capacity.
If the referendum goes ahead and the draft constitution is adopted, elections for parliament's lawmaking lower chamber will be held in February.
Associated Press reporter Sarah El Deeb contributed to this report.