The incident occurred as the man was walking along Westland Street in the Bogside of Derry at around 10 pm.
The victim required medical treatment for a bite mark to his chest as well as cuts to his face and head.
One of the attackers is described as being around 6′ tall, in his late teens or early 20s, of thin build with short dirty fair hair.
A PSNI spokesperson asked anyone who witnessed the assault or who has any information to contact police at Strand Road on the non emergency 101 tDelephone number.
Information can also be passed anonymously through the independent charity Crimestoppers on 0800 555 111.