Ahmed El-Hamrawy, head of the legal team representing the 21 female Islamist protesters handed harsh jail terms last week, disappeared early Monday.
The lawyer's wife and his defence colleague Mahmoud Gaber accused security forces of having allegedly arrested El-Hamrawy at his Alexandria home and taken him to an undisclosed location.
However, a security official denied the arrest and told Al-Ahram's Arabic news website that since El-Hamrawy does not face any charges, no arrest warrants had been issued against him.
On Wednesday, an Alexandria Misdemeanour Court handed 14 female Islamist protesters 11 years in jail and ordered seven female minors placed in a youth detention centre on charges of destroying private property, attacking security forces and stirring violence.
The defendants, who had participated in an Alexandria demonstration late October, calling for the reinstatement of ousted Islamist president Mohamed Morsi, were arrested during clashes which ensued with local residents. Authorities accused the demonstrators of inciting violence, blocking roads and damaging shop windows.
Muslim Brotherhood supporters have been staging near-daily protests since Morsi's ouster early July, while Egypt's interim authorities have cracked down on Islamists, detaining thousands of the group's members.