Armstrong was recalled from Triple-A Columbus on Tuesday.
The 26-year-old returns one day after being optioned to Triple-A with outfielder Austin Jackson (quad) heading to the DL. Armstrong has a 5.02 ERA and 1.26 WHIP with 14 strikeouts over 14.1 innings during his four stints with the Indians this season, and will likely be limited to low-leverage situations.