The victim, who was wearing a kippah, was targeted as he was leaving the building.
One of the attackers is reported to have shown the victim a picture on his mobile phone of Mohamed Merah, an Islamist militant who killed seven people, targeting French soldiers and Jewish civilians, in a series of attacks in southern France in 2012.
Although the victim suffered three knife wounds and was taken to hospital, his life was not in danger.
The attack comes just days after last Friday's terror attacks in Paris in which 129 people were killed and over 350 were injured.
Responsibility for the attacks was claimed by the Islamic State jihadist group.