Walker (blister) was placed on the 10-day disabled list Sunday, Steve Gilbert of MLB.com reports.
The Diamondbacks made the move retroactive to May 20, so there's still a chance Walker will be able to return later in the month if the blister issue subsides quickly. The timing of Walker's injury is unfortunate as he had strung together back-to-back quality starts. T.J McFarland (ankle) was activated off the disabled list Sunday and will take Walker's spot on the 25-man roster.