Former Foreign Minister Amr Moussa told The Wall Street Journal Egypt would be left with a one-party system if the Muslim Brotherhood's candidate wins the presidency and its party dominates parliament.
"It would be very destructive," Moussa said. "The (former ruling party) should not be replaced with a different color and a different hat."
He said Egypt could end up with the kind of autocratic rule that corrupted the regime of ousted President Hosni Mubarak.
Moussa noted initially the Brotherhood promised not to run a presidential candidate.
Mohammed Morsi, head of the Brotherhood's political party, joined the race at the last moment when it became clear the group's preferred candidate would likely be disqualified.
Egypt's election commission dismissed 10 candidates from the race this week.
During a campaign stop in an impoverished Cairo neighborhood, Moussa announced a program for the first 100 days in office if he wins, Ahram Online reported.
Among his priorities are updating Egyptian labor laws, reducing poverty and ensuring the rights and freedom of Egyptian women and young people.