Keller is expected to join the big-league rotation next week, Jason Mackey of the Pittsburgh Post-Gazette reports.
Per Mackey, Keller was scratched from his scheduled start with Triple-A Indianapolis on Thursday as he gears up for a promotion to the majors. The right-hander allowed six runs in each of his first two starts with the big club this season, though he performed much better in his third outing for the Pirates, allowing two runs while striking out six batters in five innings. Keller has compiled a 3.65 ERA and 67 strikeouts over his past 10 starts (56.2 innings) with Indianapolis. He'll replace Dario Agrazal -- who was optioned to the minors earlier in the week -- in the rotation. With Pittsburgh's starters set for their weekend series against the Cardinals, Keller figures to start either Monday or Tuesday against the Angels.