Walker was injured trying to break up a double play last Friday in St. Louis. He had reported daily progress in his workouts, and had an extensive workout on Friday afternoon at PNC Park, prior to the decision to place him on the DL.
The move, oddly, was influenced by an injury to another player which furthered weakened the Bucs' bench: Jose Tabata is limited by a tweak of his left hamstring, and his availability will be limited through the weekend series with the Nationals.
"You hate to throw him on the DL that quick, without giving him some down time to see what's there," manager Clint Hurdle said of Tabata. "We'll see if we can carry him through the weekend. Then we may have to do something. Tuesday is probably the day we'll have to make that decision."
Mercer was hitting .333 with 19 RBIs in 26 games with the Indians. He spent much of the 2012 season with the Pirates, often used as a defensive replacement while totaling only 62 at-bats in 42 games.