Walker has been unable to play for the past week after attempting to break up a double-play against the St. Louis Cardinals with a hard slide. The slide caused a laceration on his right hand. The move is retroactive to April 27, making Walker eligible to return to the team on May 12.
The Pirates attempted to avoid placing Walker on the DL, as he had made progress in his daily workouts since the injury. An injury to Jose Tabata, however, further depleted the Pittsburgh bench, causing them to clear space for Mercer. Pirates manager Clint Hurdle told the media that the team would wait until Tuesday to make a decision on Tabata.
Walker was swinging the bat at a league-average level the first few weeks of the season, hitting .253/.352/.342 in his first 92 plate appearances. The second baseman's average and slugging were lower than normal, but Walker had been able to compensate on offense with an above-average walk rate.
Mercer made his major-league debut for Pittsburgh last season, and hit .210/.265/.371 in 68 plate appearances. The infielder has swung the bat well so far in Triple-A this season, as he was hitting .333/.404/.448 in 109 plate appearances.