Ayman Nour, who heads the opposition al-Ghad (Tomorrow) Party, is one of a handful of challengers to President Hosni Mubarak in this year's presidential race.
Nour also accused the ruling party of trying to assassinate him in a mob attack on Thursday that killed one of his supporters and injured 20 others.
"It was a real assassination attempt. Thugs, criminals, police opened fire," Nour said at a news conference.
Nour alleged an angry mob had attacked his convoy of three buses and seven cars when he was going to inaugurate a new office for his party. He said the crowd attacked the vehicles with sticks, hurled stones and glasses filled with acid at the buses, and fired shots into the air.
Nour said he had filed a police complaint against Mubarak, as leader of the ruling party, and security authorities for the incident in Sharqiya, 80km northeast of the capital.
Protests against President
Mubarak have been growing
Nour said tough conditions set by the ruling party for independent politicians who wanted to run in presidential elections were "impossible and crippling".
He said he might pull out of the race in solidarity with the independents.
"I am considering withdrawing ... . If leaving the stage will benefit the democratic issue in Egypt, we will leave it," he said.
The elections this year will be the first with more than one candidate, after a surprise call earlier this year by Mubarak to amend the constitution to allow a more open poll.
But the new regulations outlined on Thursday by the ruling National Democratic Party, seem to limit the chance of an independent candidate winning approval to run for the presidency.
Under new rules, independents must get at least 300 recommendations from elected lawmakers.
"I am considering withdrawing. If leaving the stage will benefit the democratic issue in Egypt, we will leave it"
Parliament and the municipalities are dominated by ruling party members who are loyal to Mubarak.
The measures will ensure that the members of the anti-Mubarak Kifaya (Enough) movement and the Muslim Brotherhood - which would both have to field independent candidates as they are not recognised political parties - cannot run for president.
The amendment, which includes the rules about independents and other details, is set for a parliament vote in mid-May.