Brent (Coco) Kosolofski, 48, of Calgary, was scheduled to start his trial Thursday but instead he pleaded guilty to aggravated assault, unlawful confinement, uttering threats and robbery.
Court was told that Kosolofski and another person went to a farm near Stavely, Alta., and tried to steal several items.
A man who had some horses on the property was badly beaten when he attempted to stop them.
Kosolofski represented Canada at the 1988 Summer Olympics and later turned pro and fought for a world title.
A co-accused, Dale Corrigan of the Calgary area, faces the same charges and will be in court Nov. 19.