Three suspects have now been arrested over the "inconceivable" incident.
Three people have been detained in Greece on suspicion of attacking and kidnapping a schoolteacher who was enforcing COVID-19 restrictions.
Court authorities in the northern town of Katerini have placed three suspects in custody pending trial over the attack.
Eight other suspects have been released under conditions over the incident.
The school teacher was assaulted on Friday outside a school near Katerini, some 70 kilometres southwest of Thessaloniki.
The 61-year-old principal had been carrying out daily COVID-19 checks of students entering the premises.
Police said in a statement that a group of suspected vigilantes grabbed and handcuffed the teacher and forced him into a car.
They then drove him to local authorities and urged the police to charge him for supposedly breaching constitutional freedoms. But instead, police detained the suspected vigilantes and released the teacher.
Education Minister Niki Kerameus has said the attack was “unthinkable” and pledged to protect Greece's educational community "by all means necessary.”
The suspects — nine men and two women — face criminal abduction charges, and lesser accusations including assault, disrupting the functioning of a school, using insulting language, and breaking health regulations.
The eight released suspects must regularly present themselves regularly at a local police station, keep at least 400 metres away from schools, and cannot leave the country.
Self-styled vigilante groups have recently appeared in northern Greece, arguing that anti-COVID measures are illegal and claiming that they are defending the country's constitution.
One group recently damaged a private COVID-19 test clinic in Thessaloniki, claiming that testing was illegal. Four people were arrested and charged with impersonating authority.
The Greek government has vowed to crack down on the groups, as well as criminals selling counterfeit vaccination certificates.
Takis Theodorikakos, a Greek minister for public order, described the school incident as “utterly condemnable.”
“Such behaviour is provocative and unacceptable and the police must not allow this to be repeated,” he said on Twitter.