Robles was optioned to Triple-A Las Vegas on Tuesday, Anthony DiComo of MLB.com reports.
After struggling immensely over his last three appearances, Robles has been demoted to Las Vegas. The 26-year-old saw his ERA jump from 1.42 to 6.23 after allowing 12 runs over the last three games (2.2 innings), so he'll look to work things out with the 51's before returning to the big club. Josh Smoker was recalled from Triple-A to take his place on the roster and in the bullpen.