The assault took place in Waterworks Park in north Belfast at around 5pm on Saturday.
The 32-year-old victim was punched a number of times in the face and sustained a broken jaw.
Detective Sergeant Michael Hawthorne is appealing for witnesses to the assault to come forward:
““We would like to speak to anyone who was in the park shortly before 5 pm and who may have seen something that could assist our investigation,” said DS Hawthorne.
“Detectives can be contacted by calling 101, quoting reference 989 01/04/17.
“Or, if someone would prefer to provide information without giving their name, they can call Crimestoppers anonymously on 0800 555 111.”