[1] The Chicago White Sox selected Shirek in the 23rd round, with the 719th overall pick, of the 2007 Major League Baseball draft.
Shirek returned to Kannapolis in 2008, making 22 appearances (21 starts) and logging a 6–6 record and 3.54 ERA with 82 strikeouts over 112 innings pitched.
[3] Shirek split the 2009 campaign between the High–A Winston-Salem Dash and Double–A Birmingham Barons, accumulating a 14–5 record and 3.59 ERA with 76 strikeouts across 155+1⁄3 innings pitched.
[6] In 2012, Shirek pitched to an 11–5 win–loss record with a 3.65 earned run average (ERA) and 117 strikeouts for the Charlotte Knights of the Triple–A International League.
[7] His performance led the White Sox to add him to their 40-man roster on November 19, 2012, in order to protect him from the Rule 5 draft.