Heeney was attempting to get into a taxi when he was struck from behind.
The club released a statement on Sunday.
“The Sydney Swans are aware Isaac Heeney was involved in an unprovoked attack while in Hong Kong with teammates on Saturday morning,” the club said.
“After being taken to the closest medical facility, it was detected that Heeney had suffered a fractured jaw in the attack.”
The 19-year-old will return home to Sydney for treatment.