Gallen (elbow) will be activated from the injured list and start Thursday's game against the Giants, Nick Piecoro of The Arizona Republic reports.
Gallen last pitched May 7 before being sidelined with a right UCL sprain. He was solid in four of his five early-season starts, but control issues were a persistent problem -- he walked multiple batters in every outing and issued four free passes on two different occasions. Even so, Gallen was an ace last season and will be welcomed back to the top of Arizona's struggling starting rotation.