On Friday evening, an unidentified man attacked Nikolai Lyaskin, the head of Alexey Navalny’s Moscow campaign headquarters.

Speaking to the website Mediazona, Lyaksin said the attack took place near Navalny’s Moscow campaign office. He says the attacker hit him in the head and the shoulder. “I have an enormous bump on my head,” Lyaksin said.

According to Leonid Volkov, Navalny’s campaign manager, the campaign called an ambulance for Lyaksin. The assailant reportedly dropped the pipe and ran away, after the attack.

Alexey Navalny is running for president, hoping to find a spot on the ballot in March 2018. According to federal laws, however, he cannot stand for elected office, thanks to a suspended criminal sentence for misappropriating about $500,000 from a state-owned lumber company. Navalny denies the charges, and the European Court of Human Rights even ruled that his first conviction violated his right to a fair trial. In November 2016, Russia’s Supreme Court overturned the original 2013 sentence, but a Kirov district court repeated the verdict and sentence just three months later.