Hours earlier, security officers raided a printing press in the city and confiscated his political brochures.
Mr. Sisi has yet to declare his candidacy, although supporters say they have collected three million signatures calling on him to run. Anwar Sadat, a nephew of the former president of the same name, has indicated he will also run.
In any event, the election looks set to take place amid the harshest political repression in Egypt in decades.
Mr. Sisi has banned public protests, fragmented the opposition and exerted an iron grip on the news media.
Just last weekend, a well-known activist from Nubia, in southern Egypt, died in detention, apparently after lapsing into a diabetic coma.
On Friday, five Western ambassadors voiced rare criticism of Egypt over the detention of a human rights lawyer who was stopped at Cairo’s airport in September on his way to a United Nations meeting. On Sunday, Egypt’s Foreign Ministry summoned the ambassadors — from Britain, Canada, the Netherlands, Germany and Italy — and said their intervention was “unacceptable.”
During his news conference, Mr. Ali threatened to boycott the vote if the conditions for a fair election were not in place next year. But he might not even be able to begin his campaign if he cannot overcome a major legal hurdle first.
He faces a three-month jail sentence for public indecency that was imposed after he was accused of making a vulgar hand gesture outside a Cairo courthouse in January when he scored a legal victory over Mr. Sisi in the islands case.
An appeal against the conviction, which Mr. Ali says is politically motivated, is scheduled for Wednesday. If Mr. Ali fails, he could be disqualified from running for president.
A government-sponsored youth conference taking place in the Red Sea resort of Sharm el Sheikh this week offered critics a new opportunity to criticize Mr. Sisi. Social media activists hijacked the conference hashtag, #WeNeedToTalk, to highlight the lack of freedoms in Egypt.
The slogan circulated alongside photographs of Egyptian security forces beating protesters, or images of pro-democracy activists like Alaa Abd el Fattah, who has been in prison since 2013. Some focused their ire on the actress Helen Hunt who addressed the conference on Sunday, accusing her of legitimizing Mr. Sisi’s rule.
“As you shake hands with Sisi,” wrote leading members of Egyptian civil society in an open letter to Ms. Hunt, “let history note that you chose to support a dictator responsible for thousands of deaths, arbitrary detentions and disappearances.”
Stephen Huvane, a spokesman for Ms. Hunt, said in an email on Monday night that Ms. Hunt “did not meet with the president and did not shake his hand. She was there to attend the youth conference along with several other amazing men and women.”
“The event was meant to encourage open dialogue and was not any endorsement of the president,” Mr. Huvane said.
Mr. Ali also ran for president in 2012, but then he was a little-known leftist and won few votes. But his profile rose last year after he led a powerful protest movement challenging Mr. Sisi over his decision to hand over the Red Sea islands of Tiran and Sanafir to Saudi Arabia.
Widespread public anger over the islands signaled a rare moment of vulnerability for Mr. Sisi. Protesters led by Mr. Ali stopped the transfer through a legal challenge. But in June the transfer was approved by Parliament, which is stuffed with Sisi supporters, and days later the president hastily signed it into law.
Saudi Arabia’s interest in Tiran and Sanafir became clearer last month when the Saudis announced plans for a futuristic city that would be partly built on the two disputed islands.