A police officer has faced court charged with assaulting a man in custody at a Sydney police station

A Sydney police officer who allegedly assaulted a man so badly he ended up in hospital has faced court.

A 52-year-old man was in custody at Redfern Police Station when he was allegedly assaulted by a male constable in June.

The man was treated at St Vincent's Hospital and released the next day.

The officer, who is suspended on pay, was charged in early November with common assault and assault occasioning actual bodily harm.

He faced court on Monday and will return to the Downing Centre on February 6.