The Cardinals recalled Walker from Triple-A Memphis on Friday.
Walker went 1-for-11 during a six-game span with the Cardinals earlier in August, but 10 days after being optioned to Memphis, he returns to the 26-man roster. The 22-year-old outfielder replaces Tommy Pham, who was designated for assignment in a corresponding move. Walker is 10-for-69 (.145) with a triple, four doubles, four runs and four RBI this season with St. Louis and while he'll like be deployed primarily against left-handed pitching in the short term, he could get a chance to start if St. Louis fades out of the playoff picture.