The Orioles recalled Walker from Triple-A Norfolk on Friday.
The 31-year-old acted as the 27th man during Wednesday's doubleheader against Boston before being returned to Triple-A, but Walker hasn't actually pitched in a big-league game since June 30. With Norfolk, the left-hander has posted a 3.73 ERA, 1.05 WHIP and 34:10 K:BB in 31.1 innings.