"Some man burst into the building, blinded the building's security guard from a spray bottle, then came up to our floor," said Echo of Moscow editor-in-chief Alexei Venediktov.
"He broke in and stabbed our presenter Tatiana Felgengauer in the neck with a knife," he told AFP. "My security guards overcame him, and we handed him over to the police."
The journalist has been hospitalised but her life is not in danger, he said.
Another station employee Vitaly Ruvinsky posted on Twitter a photo of the dishevelled man dressed in a black jacket and trousers seaten in a chair.
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Felgengauer is one of the station's deputy editors and a longtime presenter of a morning news programme. She is also actively involved in opposition rallies and has thousands of followers on her public Facebook page.
Echo of Moscow is a well-known station that regularly invites Russian political opposition figures and is known for its critical views of the government despite energy giant Gazprom being the majority shareholder.
Another Echo of Moscow presenter Yulia Latynina this year left Russia after a series of attacks on her car and home.