The victim was walking alone along Thabahandi Street at around midnight, when he was struck on the back of the head.
Capt Mandla Phori of KwaThema police says the victim explained after being hit, he immediately fell to the ground.
He then saw three men armed with beer bottles.
The men assaulted the man and robbed him of his cellphone.
The man suffered serious injuries to his head and was taken to Pholosong Hospital.
Police are investigating a case of robbery and Phori says a 22-year-old suspect has since been arrested.
If you can assist with the investigation contact KwaThema police on 011 812 4600.
