With the Padres' relief corps in need of a respite, Diaz was activated before Tuesday's game, with shortstop Dusty Coleman optioned to El Paso. Diaz will likely be used out of the 'pen over the next couple of days, though it's still a possibility he returns to the rotation next month.
"Right now he's in the bullpen," Padres manager Andy Green said. "We've thought about bringing him back in the rotation, but we got to a point where we needed [relief help]."
Diaz, the top overall selection in the Rule 5 Draft, began the season as a reliever before transitioning to the rotation.