After finishing his junior season with the Loyola Marymount Lions, Donnels emerged as one of the best hitters in the West Coast Conference in 2014. In 56 games, Donnels hit .321 with a home run and 36 RBI. Donnels also stole eight bases, and possessed a .985 fielding percentage.
In 2013, Donnels played in 51 games, hitting .245 with 22 RBI and five stolen bases. In his freshman season (2012), he hit .246 with a home run and three RBI in 25 games.
Before beginning his career at Loyola Marymount, Donnels played baseball at Tesoro High School (Rancho Santa Margarita, CA). In his senior season, he hit .314 with 10 RBI, helping the team perform well in California interscholastic competition.