The unidentified 27-year-old, accompanied by a friend, got so close to the Siberian tiger's fencing, it grabbed him and inflicted serious claw and biting injuries, the Calgary Herald reported.
The man was attacked about 1 a.m. Monday. Police said they suspect the pair scaled the zoo's outer fence and then a second one that keeps big cats at a distance from visitors.
The report said the uninjured man then called his friend's wife, who works at the zoo as a security guard and called 911.
Breaking-and-entering and trespassing are among the charges being considered once the hospitalized man comes out of sedation, the newspaper said.