The 18 year old was briefly knocked unconscious during the fight, that broke out in Liberation Square at around 1:15am.
One man was arrested at the scene and bailed while investigations continue.
Jersey Police want to speak to anyone in the area at the time, particularly two men seen talking to the pair involved in the fight immediately before it happened.
The force says it’s also keen to track down another man who may have recorded the incident on his mobile phone.
Anyone with any information is asked to contact police on 612612 or the independent charity Crimestoppers anonymously on 0800 555 111 or via their anonymous online form at Crimestoppers-uk.org.