The 22-year-old rookie will get his second and final start since taking the place of the injured Roenis Elias after throwing 5 2/3 innings of two-run ball in a 10-5 win at Houston on Friday. Walker is regarded as the Mariners' top prospect.
Buehrle will need another six innings in his final start of 2014 to reach 200 frames for the 14th straight season. Manager John Gibbons said he will do everything he can to help Buehrle reach that mark.
This was to be Chris Young's turn, but the veteran right-hander was removed from the rotation on Monday.