Police were called to the incident at 4.24pm on Thursday to reports of a fight in the fast-food chain on Lewisham High Street.
Officers found a member of staff with facial injuries and lacerations to the back of the head.
A McDonald’s spokesperson told The Standard: “The safety and security of our people and customers is our absolute priority. Violence has absolutely no place in our restaurants, and we are shocked and appalled by this behaviour.
“The police were called immediately to the incident, and we are assisting them with any enquires. We have remained in regular contact with the employee in question, and are offering him, and other members of the restaurant team, all the support they require.”
The London Ambulance Service also attended the scene but the man’s injuries were not life threatening.
So far there have been no arrests.
A McDonald’s spokesperson told the Standard: “The safety and security of our people and customers is our absolute priority. Violence has absolutely no place in our restaurants, and we are shocked and appalled by this behaviour.
“The police were called immediately to the incident, and we are assisting them with any enquires. We have remained in regular contact with the employee in question, and are offering him, and other members of the restaurant team, all the support they require.”