Armstrong was optioned to Triple-A Columbus on Friday.
In a corresponding move, Cleveland recalled left-hander Ryan Merritt from Columbus prior to his spot start against the Royals. Armstrong was only just called up by the club a couple days ago, but gave up two earned runs in 1.1 innings against Boston on Tuesday in his lone appearance. The 26-year-old will likely be back with the Indians once rosters expand next week, serving in low-leverage situations out of the bullpen.