The Oakland A's placed Kyle Muller on the 15-day injured list and recalled fellow left-hander Hogan Harris from Triple-A Las Vegas on Thursday.
Muller, 26, is dealing with tendinitis in his pitching shoulder. The reliever has not appeared in a game since last Friday and his IL designation is retroactive to Monday.
Muller is 0-1 with a 3.48 ERA in 13 relief appearances this year, striking out 24 batters and walking seven over 33⅔ innings. He is 4-11 with a 5.97 ERA in 46 games (24 starts) with the Atlanta Braves (2021-22) and Athletics.
Harris, 27, made two appearances out of the bullpen for Oakland earlier this month and allowed four earned runs on eight hits in 8⅔ innings. He is 1-2 with a 7.67 ERA in eight games (all starts) for Las Vegas.