Rookie right-hander Carlos Martinez was optioned to Memphis.
The 27-year-old Rzepczynski was demoted to the minors April 29 and was 1-2 with a 3.07 ERA at Memphis while limiting left-handed hitters to a .185 batting average. Rzepczynski appeared in 70 games with St. Louis last season.
The 21-year-old Martinez was the organization's minor league pitcher of the month in June and is among their top prospects for a future rotation spot. He has a 5.56 ERA in 10 games covering 11 1-3 innings with St. Louis.