The North East Ambulance Service (NEAS) said its team had been attending an incident in Washington, near Sunderland, on 17 July.
The attacker fled before police arrived.
Northumbria Police said it had launched an investigation and was trying to locate the man.
NEAS said the whole organisation had been impacted by the staff member being unable to return to work because of their injuries.
‘Hundreds of incidents’
Chief operating officer Stephen Segasby said: “Physical and verbal abuse of our people is completely unacceptable.
“Our staff report hundreds of incidents every year that put them at risk. Assaults have a significant impact on the physical and mental health of the people who help us deal with an emergency.
“For our colleagues, working for the ambulance service is so much more than a job.
“They come to work to help people and under no circumstances should they expect to find themselves a victim of any form of abuse whilst trying to do so.”
Ch Insp Neil Hall, of Northumbria Police, said attacks would “not be tolerated”.