Levan Khabeishvili, the leader of the main opposition in Georgia, was beaten during last night's protest against the bill on foreign agents in the capital Tbilisi, Reuters reported , quoted by BTA, referring to a representative of the "United National Movement" party.
Habeishvili disappeared during the demonstration, after which it became clear that he had been beaten.
The party representative also said that Khabeishvili is receiving medical assistance.
Georgian media published photos showing Khabeishvili's face bloodied and his eye bruised.
Georgian police resorted to force against demonstrators, reported France Press.
Police officers specialized in fighting riots intervened without warning and used tear gas and rubber bullets against the demonstrators, beating and arresting dozens of people, an AFP journalist found.
Earlier in the evening, demonstrators gathered in front of the Parliament building to protest against the bill on "foreign influence", which they believe violates civil liberties.
Brussels said the text jeopardized Georgia's bid to join the European Union.
The ruling party "Georgian Dream" has been trying since April 9 to push the bill through after failing to do so last spring, when there were also large protests against the planned legislation.
Critics of the bill say it is inspired by Russia's law on foreign agents, which is used by authorities to silence dissidents, notes AFP.
There were also demonstrations against the bill in the second largest Georgian city of Batumi.
The President of the European Council, Charles Michel, said that the bill is not compatible with Georgia's desire to become part of the EU.