Foltynewicz, acquired in the January trade that sent slugger Evan Gattis to Houston, began the season as the top-rated pitcher in Atlanta's farm system. After getting called up from Gwinnett on May 1, he went 3-2 with a 5.19 ERA in his first nine career starts.
Foltynewicz went 0-0 with an 8.04 ERA in his past three starts, giving up 29 hits and four homers.
Manager Fredi Gonzalez said Foltynewicz, whose average fastball hits 97 mph, will likely return to Atlanta's rotation at some point, but he wouldn't specify when.
The Braves selected the contract of infielder Daniel Castro from Gwinnett to replace Foltynewicz on the 25-man roster.