Walker will report to Triple-A Indianapolis on Tuesday after the Pirates acquired him from the Mets in exchange for left-hander Nicolas Carreno, Andrew Destin of the Pittsburgh Post-Gazette reports.
The 29-year-old has tossed 28.2 innings at the Triple-A Level this season, posting a 2.83 ERA and a 39:21 K:BB. He may need to show more improvement with his control at Indianapolis before the Pirates open up a spot for him in the big-league bullpen.