The attack by the rodents is said to be so bad that health and safety officers have told them to take precautions, which also included making loud noises to scare them off.
According to the shocked district nurse, who was left with "reddening of the scalp" after being targeted, the squirrel attack was rated as "moderate" on a scale of "insignificant to catastrophic".
"On walking up farm access I was jumped upon by a squirrel. Then another landed on my head," the Mirror quoted her as having written in the report.
But bosses regarded the incident as serious and sent a report to the Department of Health in London, where safety chief Gregor Miller said that the nurse was shaken after the attack near Langley Park, County Durham.
"It's not every day you are attacked by a squirrel. It was a garden grey as far as we're aware," he said.
"There were two of them, but they don't seem to hunt in gangs. We've had no other reports of squirrels - probably in hooded jackets - attacking staff," he added.