Police have released images of a man wanted over the robbery of a skateboarder, who suffered serious head injuries when he was struck over the head with his own board in Sydney.

The 21-year-old skateboarder was knocked unconscious in the assault on Oxford Street in Darlinghurst in December.

Police want to speak with this man over the assault of a Sydney skateboarder.

Police on Wednesday released CCTV images of a man they would like to question over the assault, which occurred about 5.20am on December 7.

The skateboarder told police he was walking west along Oxford Street, near Liverpool Street, when he was approached by a man who struck up a conversation with him.