Right-hander Jake Westbrook, who has struggled for several starts, is being placed on the 15-day disabled list by the St. Louis Cardinals because of a lower back strain.
The move, announced on Friday, is retroactive to Thursday.
Rookie right-hander Carlos Martinez was recalled from Triple-A Memphis and could take Westbrook's spot in the rotation.
In his last five starts, Westbrook has given up 30 earned runs in 26 innings. He was on the disabled list earlier this year with an elbow injury.
The 21-year-old Martinez made his first career major league start on Aug. 8 against the Dodgers and is 0-1 in 11 games with St. Louis. He is 5-3 with a 2.66 ERA in 12 starts at Memphis.