Villarreal missed most of due to a sore elbow, and later elbow surgery. He appeared on Opening Day against the Rockies, and did not allow any runs. In the month of April, he recorded 15 strikeouts in 12.1 innings, while only walking one batter. Villarreal was placed on the disabled list on May 10 with a strained right flexor. After playing on a rehab assignment with the Tucson Sidewinders in July, doctors took an MRI on Villarreal's elbow on August 6 and determined that he would need to undergo season-ending nerve transposition surgery.