McDonald began his junior career in 1969 with the Lethbridge Sugar Kings of the tier II Alberta Junior Hockey League (AJHL). He appeared in 34 games for the Sugar Kings as a 16-year-old, scoring two goals. The following season, 1970–71, he emerged as a leading scorer, recording 37 goals and 82 points in 45 games. He was voted the league's most valuable player and named to the Second All-Star team. Additionally, McDonald appeared in six WCHL games with the Calgary Centennials.