Silseth was optioned to Double-A Rocket City on Tuesday, Jeff Fletcher of The Orange County Register reports.
The 22-year-old delivered six shutout frames during his major-league debut in mid-May, though he surrendered nine runs over 10.1 innings across his past three starts and will now return to Rocket City. Silseth, who is the Angels' top prospect, could receive another big-league opportunity at some point this season, but for now he'll make his way back to Double-A. Jose Suarez was recalled in a corresponding move and is starting Tuesday versus Boston.