Walker was removed from Tuesday's Grapefruit League game against the Nationals in the third inning with a pain in his left knee, Katie Woo of The Athletic reports.
Walker appeared to tweak his knee while chasing down a flyball in the second inning, as he was seen grimacing and grabbing at his leg after the play. He struck out in his lone plate appearance before exiting. Walker will be re-evaluated once the Cardinals return to their spring training complex.