The journalist, Anna Pozdnyakova, claims Udaltsov hit her during an interview at anti-NATO rally in Ulyanovsk on April 21.
Udaltsov has denied he attacked Pozdnyakova, who is an activist in the pro-Kremlin Young Guard movement.
A video appeared on YouTube allegedly showing Udaltsov hitting Pozdnyakova.
Udaltsov’s wife reportedly placed a video clip on his twitter page that shows there was no assault.
Udaltsov was just released from detention after serving a brief jail term for resisting arrest at a demonstration in early May.