Villarreal has been a long-time pitcher for the Reds toward the top of the organization, making his debut during the 2012 season. He was originally a seventh round pick in the 2008 draft by the Reds. He has seen time out of the Reds bullpen in each season from 2012 to ’15, posting a 4.29 ERA over that time with a 1.44 WHIP. He has solid command, but he has played very hittable at the big league level. The Reds non-tendered Villarreal and re-signed him to a Minor League deal prior to the 2016 season. He took some time to rise up the ranks in the organization, earning a promotion to Triple-A in 2012, but had the ability to stick at the level.