Police said the lone patrol officer stopped a vehicle near Wanham, Alta., after reports it had been driving erratically.
While details remain unclear, it appears the driver and officer then became involved in an altercation resulting in the officer being injured and left in the ditch.
Truck driver Jonathan Hiscock pulled up shortly after the incident took place, and spoke with one of the volunteer emergency responders on the scene.
“[He] informed me that the officer that was doing a routine stop and ... when everything was seeming to be OK, apparently the assailant came out of the vehicle and actually attacked the officer, strangling him, and brought him right into the ditch where the officer was left,” said Hiscock.
“Presumably, he was left for dead,” he added.
The officer was taken to hospital where he remains in stable condition.
“We don't know the extent of the injuries," Cpl. Carol McKinley told CBC News on Wednesday night.
“We’re certainly canvassing the public for any information that will help provide us with some further avenues and encourage anyone to contact either our Spirit River detachment or Crime Stoppers,” she added.
Hiscock, who lives in the area, called the incident “shocking.”
“Even the people who were around there – the emergency response – everybody was just blown away. This just doesn’t happen,” he said.
The name of the RCMP officer has not been released.
Wanham is about 480 kilometres northwest of Edmonton.