Updated with Volkov's comments.
Longtime Navalny aide and former Anti-Corruption Foundation (FBK) chairman Leonid Volkov was attacked at his home in Lithuania on Tuesday night, his associates said.
"Someone broke a car window and sprayed tear gas in his eyes, after which the attacker started hitting Leonid with a hammer," Navalny's spokeswoman Kira Yarmysh wrote on X, formerly Twitter.
Volkov, who has lived outside Russia since Moscow designated Navalny's groups as banned "extremist" organizations in 2021, was later briefly hospitalized.
Early Wednesday, Volkov, 43, vowed to continue his struggle against President Vladimir Putin.
"We will work and we will not give up," he said in a video clip published to his Telegram channel, adding that the attack that left him with a broken arm was a "characteristic bandit hello" from Putin's henchmen.
"The man attacked me in the yard, hit me on the leg about 15 times. The leg somehow is OK. It hurts to walk... However, I broke my arm," Volkov said.
"They literally wanted to make a schnitzel out of me."
Another longtime Navalny aide, Ivan Zhdanov, published photos of Volkov after the attack on the Telegram messaging app.
In one of the photos, Volkov's leg can be seen covered in blood, while another photo showed a car with its window smashed.
An image posted shortly after showed him being carried on a stretcher and placed inside an ambulance.
It was not immediately clear who the assailants were.
Lithuanian police said Wednesday they were investigating the attack.
"We are taking all steps to clarify the motives and causes of the crime. Several versions are being investigated," deputy chief of police Saulius Tamulevicius told local media.
Last year, Volkov unexpectedly stepped down from his role at the FBK after he was forced to publicly admit to writing a letter in defense of sanctioned Russian billionaire Mikhail Fridman.
The letter, which he signed on behalf of the opposition organization, called on the EU to lift its sanctions on Fridman and other prominent shareholders in his Alfa Group consortium in an alleged attempt to fuel divides within Russia’s political elite.
AFP contributed reporting.