Hours before a nomination deadline was set to make President Sisi the sole candidate, Mousa Mostafa Mousa tossed his hat into the ring.
Several leading opposition figures called on Sunday for a boycott of the March election, citing a wave of repression that has cleared the field of challengers to Sisi and left his top opponent in jail.
Former military commander Sisi was elected in 2014, a year after leading the army to oust Islamist President Mohamed Mursi. He is expected to easily win the vote, the third since protests in 2011 unseated long-time ruler Hosni Mubarak.
Mousa, who leads the Ghad party, told Reuters he was at the electoral commission registering his candidacy after having collected the required number of nomination pledges.
Would-be candidates are required to register by 2 pm on Monday after clinching at least 20 nominations from parliament or 25,000 pledges from citizens across the country.