Left-handed reliever Ian Thomas was optioned to Triple-A Gwinnett to make room on the 25-man roster for Simmons. The Braves will have to make another move to clear a spot on the 40-man roster for their newest reliever.
Simmons, ranked 17th on the Braves' Top 20 Prospects list, has posted an 0.78 ERA and recorded 30 strikeouts while issuing just six walks in 23 innings for Double-A Mississippi this year. The hard-throwing right-handed reliever has limited opponents to a .183 batting average. Right-handed hitters have hit just .163 (8-for-49) against him.
While Simmons is likely targeted to stay in Atlanta for the remainder of this season, the need to call him up to the Majors has been hastened by the bullpen struggles experienced this week. A few of the late-inning collapses have highlighted how much the relief corps misses right-handed setup man Jordan Walden, who has been sidelined since May 4 with a strained left hamstring.
The Braves have been encouraged with the progress Walden has made while throwing off a mound at the club's Spring Training facility this week. But he is not expected to return for at least another week, and it remains to be seen how stable his leg proves to be when subjected to his violent delivery on a regular basis.
Simmons made a quick Cinderella rise to the Majors. The Braves selected him out of Southeast Missouri State in the 22nd round of the 2012 First-Year Player Draft.
Mark Bowman is a reporter for MLB.com. Teddy Cahill is a reporter for MLB.com. Follow him on Twitter at @tedcahill. This story was not subject to the approval of Major League Baseball or its clubs.