Four police were charged last week over the incident, one remanding in custody before trial.
The remanding in custody of a French policeman in the city of Marseille sparked new controversy Monday weeks after violent riots, with the left lambasting a call from police chiefs for the officer to be freed.
France was rocked by over a week of riots that began last month over the killing of 17-year-old Nahel M. by a policeman during a traffic check outside Paris. The officer has been charged and jailed ahead of trial.
In the incident in Marseille, a man named as Hedi, 21, says he was beaten by four or five men he identified as police during unrest in the city over the death of Nahel M. earlier this month.
He says he was also hit in the head by a blast ball fired by police. He underwent operations and has now returned home but risks losing the sight in one eye, according to his lawyer.
Four police were charged last week over the incident, one of whom was remanded in custody ahead of trial.
"Knowing that he is in prison is stopping me from sleeping," said France's national police chief Frederic Veaux in an interview with the Le Parisien newspaper published on Monday.
"In general, I believe that ahead of a possible trial, a police officer should not be in prison, even if he may have committed serious faults or errors in the course of his work," he added.
Paris police chief Laurent Nunez tweeted that he shared the stance of Veaux.
According to a union source, who asked not to be named, several hundred Marseille police officers have gone on sick leave in a sign of protest over the officer's detention.
Others responded to the call of the SGP Police Unit union and put themselves under so called "code 562" which means that they only respond to emergency and essential missions.
But hard-left France Unbowed (LFI) leader Jean-Luc Melenchon said France's leaders were refusing to call on the police "to respect the law" and police were instead given a green light to "wage war".
"It's extremely serious, the entire police hierarchy places itself above justice and the rules of pre-trial detention," added Socialist Party chief Olivier Faure.
"What is at stake here is democracy and respect for the rule of law. Parliament must be reconvened urgently," he added.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)