Walker was removed from Monday's game against the Nationals after three innings due to left oblique tightness. He struck out in his lone plate appearance before exiting the contest.
An explanation behind Walker's early departure wasn't immediately known when Kevin Newman came off the bench to replace him in the top of the fourth inning, but the Diamondbacks provided clarity on the matter shortly thereafter. The fact that the injury is to the right-handed hitting Walker's left side isn't a great sign, but the Diamondbacks will wait and see what further tests reveal before providing a prognosis for the 33-year-old first baseman.