Valdez was optioned to Triple-A Worcester on Thursday, Jen McCaffrey of The Athletic reports.
Valdez has spent a significant amount of time in Boston this season, but he'll return to the minors to make room for Hansel Robles (back), who was activated from the injured list in a corresponding move. Valdez has a poor 5.84 ERA across 12.1 innings in the majors, though his 3.71 FIP indicates that he's deserved better results.