Tarek El-Zomor has threatened to use violence if President Morsi is forced from power.
“The voice of violence shall prevail above everything else,” said El-Zomor, official spokesperson of Al-Gamaa Al-Islamiya's Construction and Development Party, in a statement released on Thursday.
El-Zomor’s threat comes before nationwide protests scheduled for 25 January to celebrate the second anniversary of Egypt's revolution.
He said that he was ready to fight any opponents of the Islamist current.
President Morsi was elected and can only be removed via the ballot box at the next presidential election in 2016, he added.
“If the president is forced out of power through illegitimate means, the Muslim Brotherhood, which is known to be peaceful, would have to step aside for revolutionary Islamists to fight the anarchists and secularists,” El-Zomor said.
“In this case, martyrdom will be the least we can offer to fight the communists, secularists and Nasserists,” he said. “They are jealous of the Islamists and their Islamic project.”