Hoshiar Bajwa, 65, was on shift at the construction site at the Pitt River Community Middle School on Tyner Street when he reportedly saw a man jump the fence.
When he went to talk to the man, two other men came up behind him and smashed his head with a metal bar from the construction site.
The trio then beat Bajwa for some time before leaving him lying on the ground covered in blood, according to Rupinder Sagoo, the operations manager for Canuck Security, who arrived at the site shortly afterwards.
"They just hit him in his head a couple times, and all three guys started beating him, badly beating him. And afterward they just left, they just climbed the fence and left," said Sagoo.
"He was badly hurt, like all the bleeding and stuff from the head, and his right eye was also having swelling."
Bajwa received over a hundred stitches and is recovering in hospital, but may lose his sight in one eye because of the attack, according to reports.
Sagoo says Canuck Security management will meet today to discuss ways to improve security for its security guards. In the meantime Sagoo said he was nervous about taking over the shift after the beating.
"I was also a little terrified, because I have seen his blood, I have seen his injury and everything," he said.