The Cardinals placed Walker on the 10-day injured list Saturday with left wrist inflammation, retroactive to Thursday.
Walker's wrist injury helps to explain why he was left out of the lineup Friday against Arizona. The severity of his injury is still unclear, so there's no telling if he might be able to return when eligible June 8. In the meantime, Ryan Vilade will come up from Triple-A Memphis to replenish St. Louis' outfield depth.