Armstrong was recalled from Triple-A Columbus on Tuesday, Zack Meisel of Cleveland.com reports.
Armstrong will join the Indians for the first time this season after he dealt with back issues during spring training. The right-hander, who appeared in eight games for Cleveland last season, is off to a strong start at Triple-A -- 2.50 ERA, 15 strikeouts per nine innings -- but he continues to struggle a bit with control, issuing 17 free passes in 18 total innings. Armstrong will take the spot of Ryan Merritt, who was optioned to Triple-A on Tuesday morning.