A man had to be taken to hospital after sustaining a head injury during a fight at the McDonald's restaurant on the corner of King and Steel streets on Sunday.
Paramedics and police were called to the 24-hour fast food outlet in Newcastle West about 3am after reports of a fight in the car park.
A NSW Ambulance spokesperson said a man believed to be aged in 20s had his head injury treated at the scene before being transported to John Hunter Hospital in a stable condition.
The man was a security guard contracted by McDonald's.
A statement from the company said the incident occurred after two individuals carrying alcohol were refused entry to the store.
"A member of the security team was advised to go to the hospital for observation purposes only," it said.
Police are investigating the incident.
The 24-hour store is a popular haunt for late-night partygoers.
Following a brawl at the fast food outlet last month, McDonald's Australia told the Newcastle Herald it was implementing measures to help reduce anti-social behaviour, including temporary car park closures and increasing security.