Four paramedics were rushed to hospital after they were attacked while trying to help a patient who had collapsed on the street.
The London Ambulance Service said a crew was called to a help an "unconscious patient" in a street in Croydon town centre, south London, on Saturday (27 January).
The four medics were confronted by a 25-year-old man who "became aggressive towards the crew" and assaulted them, said the service.
Incident response officer Tim Gerhard was sent to the scene and all the paramedics were taken to Croydon University Hospital and treated for minor injuries.
Peter McKenna, deputy director of operations for the London Ambulance Service, said: "I am appalled by this attack on our staff. The person responsible has been arrested and we are working with the police. Attacks like this are totally unacceptable.
"This senseless attack also resulted in even more pressure being put on the service as four medics were taken off the road to receive medical treatment and provide statements to the police."
The Metropolitan Police said a 25-year-old was arrested on suspicion of assault and actual bodily harm and remains in custody.
It is understood that the suspect was the person the medics had originally been sent to helpt.