A patient reportedly "kicked" and "spat at" Gloucestershire Royal Hospital staff after being taken there by the ambulance service.
Gloucestershire Police are appealing for witnesses after the assault, which was reported to have happened on Thursday 10 March between 3.30pm and 4pm.
A spokesperson from the force said the man has been described as white, around 5ft 10ins tall, bald, wearing blue jeans, a black jacket and trainers.
He was detained at the hospital and arrested on suspicion of assault, but has since been released under investigation.
Any witnesses or anyone with information is asked to get in touch with police by completing this online form and quoting incident number 255 of 10 March.