The Cardinals released Parker from his minor-league contract Thursday, Jeff Jones of the Belleville News-Democrat reports.
Parker was reassigned to minor-league spring training Friday.
Parker signed a minor-league contract that includes an invitation to spring training with the Cardinals on Saturday, John Denton of MLB.com reports.
Parker (2-1) allowed a run on one hit and struck out three in 1.1 innings, taking the loss Tuesday versus Kansas City.
Parker allowed two hits and struck out two in a scoreless inning during Sunday's 11-1 win over the Yankees.
Parker (2-0) walked one and struck out one in one inning, earning the win Wednesday versus Kansas City.
Parker has allowed two runs in 11 innings in August.
Parker logged two scoreless innings, allowing a hit and striking out one in Monday's 9-3 win over Cleveland.
Parker has allowed just one run across 7.1 innings in July.
Parker allowed a hit and struck out one in a scoreless inning in Game 2 of Wednesday's doubleheader versus Tampa Bay.