According to the organization's sources, at around 12.50 p.m., two men, with their faces covered and carrying a baseball bat and a long knife, attacked Jimmy Sham and a friend at a restaurant in Kowloon area, Efe news reported.
Although Sham was unharmed, his friend, who tried to protect him, received three blows with the bat and had to be taken to a hospital. No further information has been revealed about his condition, although photos that have been published reveal a bruised arm.
Local police sources told Efe news that "preliminary investigations" of the incident suggest that the assailants were of a different nationality and not Chinese.
The South China Morning Post newspaper identified the injured man as Law Kwok-wai, who was Sham's collaborator.
In recent months, CHRF has been responsible for organizing the biggest demonstrations in the city, including three that they say were attended by more than 1 million people.
Earlier on Thursday, pro-government demonstrators staged a protest before the CHRF headquarters to condemn its participation in the aforementioned marches, terming Sham a troublemaker and tried to snatch a megaphone from him.
According to the island's public broadcaster RTHK, this group of protesters dispersed after the police arrived on the scene.
The march convened by CHRF for Saturday was banned early Thursday by the authorities, who alluded to episodes of violence recorded in previous demonstrations to justify the decision, according to the South China Morning Post.
CHRF had sought a rally on Saturday at 3pm local time in Hong Kong's central Chater Park, followed by a march to the headquarters of the Liaison Office, the body that officially represents the Beijing government in the autonomous city.
Sham said he would appeal against the police ban, although he expressed little hope in it being overturned.
The demonstrations have resulted in the mobilization of hundreds of thousands of people since June, and have been accompanied by police repression in order to thwart attempts to disrupt the normal course of the city with strikes and occupation of its public spaces.
Although they began in opposition to a contentious extradition bill, the lawsuits have expanded and call for an improvement in the city's democratic mechanisms.
Since June, Hong Kong has been in the throes of its worst political crisis in decades, sparked by the now-shelved extradition bill that would have enabled suspects to be extradited from Hong Kong to mainland China to face trial under Beijing's judicial system.
( With inputs from IANS )