The assault at the St Martin’s pub happened at around 19:40 on Sunday.
Guernsey Police would like to speak with any members of the public who were present at the time.
Anyone who witnessed or has other information about what happened is asked to contact PC 68 Winberg or PC 77 Taylor at the police station on 222 222.
Alternatively, people contact CrimeStoppers anonymously on 0800 555 111.