Muller will be recalled from Triple-A Gwinnett to start the first half of Saturday's doubleheader against the Marlins.
Muller has a 5.49 ERA in 39.1 career major-league innings, but the 24-year-old lefty has looked quite good in 17 starts for Gwinnett this season. He's struck out 31 percent of batters while walking just 6.9 percent, leading to a 3.27 ERA. It's unclear whether or not he'll have a chance to push for a starting role down the stretch or if he'll return to the minors immediately after Saturday's game.