ORONO — Authorities have identified the bicyclist who was severely injured after being struck in the left leg by a sharp-edged, 8-foot-long tractor saw used to mow lawns.

Margaret Nagle, spokeswoman for the University of Maine, identified the rider as Nathan Godfried. Godfried has taught history at the Orono campus for the last 17 years.

His leg had to be amputated after the accident, Nagle said.

The Penobscot County Sheriff’s Department said Godfried was riding his bicycle along Route 2 in Passadumkeag on Sunday afternoon when a truck that was towing a trailer with a John Deere tractor on it attempted to pass him.

Police said the truck’s driver was unaware that the saw had become dislodged and instead of being in an upright position was sticking out to the side of the road. The mowing attachment struck Godfried in the leg.

A nurse, who happened to be driving past the accident scene, pulled over and was able to stop the bleeding until an ambulance crew arrived. Police said she probably saved Godfried’s life.

Godfried, who is a scholar in 20th-century American pop culture, is married to Elizabeth McKillen, a professor of history at the University of Maine.

Deputy Ryan Fitch, who investigated the mishap, said he is not planning to charge the driver of the truck.

“It was just a freak accident,” Fitch said.