Prior to beginning his professional career, he played college baseball at the University of California, Irvine.

Cassel attended Chatsworth High School, where he set single season records in wins, strikeouts and shutouts.

[3] Cassel was then selected by White Sox in seventh round (225th overall) of 2006 Major League Baseball draft.

In 2007, Cassel pitched for the Bristol White Sox of the Rookie-level Appalachian League and Winston-Salem.

In 2008, playing for the Class-AA Birmingham Barons, Cassel was named to the Southern League All-Star team.