It happened in the Beechmount Parade area of West Belfast in the early hours of Friday 26th December.
Detective Sergeant Melanie McGrory said, “ A man in his 20’s was assaulted in the street, at Beechmount Parade, just before 6am on Friday morning.
“He has been unable to give a description of the person or persons involved at this time, or if a weapon was used.
“Following medical attention at hospital the man was found to have suffered a fractured skull.
“I am appealing to anyone with any information about this incident to contact CID at Woodbourne on 101. Information can also be passed anonymously through Crimestoppers on 0800 555 111.”