Underwood was assigned to minor league camp Monday, Patrick Mooney of CSN Chicago reports.
The 2012 second-rounder received an invite to major league camp but was never considered a serious contender to make the Opening Day roster. Underwood will likely begin the year at Double-A after splitting the 2015 campaign between Rookie ball and High-A. In 14 appearances for High-A Myrtle Beach, Underwood posted a 2.58 ERA across 73.1 innings.