The Committee To Protect Journalists (CPJ) says Ukrainian authorities "need to act urgently" to protect journalist Oleh Bogdanov.
Bogdanov was severely beaten by unidentified attackers near his house in the eastern city of Donetsk on July 21.
He was hospitalized with a broken jaw, a broken nose, and concussion.
Bogdanov works for the website Dorozhny Kontrol (Road Control), which reports on abuses committed by Ukrainian traffic police and other law enforcement agencies.
Bodgdanov told Ukraine's Channel 5 television that he believes the attack was connected to his work.
The CPJ's statement on July 22 said Bogdanov has been subjected to threats and an arson attack on his car.
The CPJ's Nina Ognianova called for the authorities to launch "an independent and effective investigation."