Westbrook pitched for Class A Peoria on Sunday, and looked effective in what is expected to be his final rehab start. The veteran threw seven innings, allowing one run on 76 pitches.
The Cardinals placed Westbrook on the 15-day disabled list on May 12 with elbow inflammation. The starter told the Associated Press that he had been dealing with the elbow pain since Spring Training, and decided it was time to give his arm a rest.
The 35-year-old made six starts for St. Louis before heading to the DL, going 2-1 with a 1.62 ERA. Westbrook forced opposing batters to hit the ball on the ground 61.3% of the time, the second-highest groundball percentage among starting pitcher's in MLB.
Tyler Lyons is currently scheduled to pitch for the Cardinals on Friday. Lyons has made four starts, going 2-2 with a 3.51 ERA. The team could keep Lyons in the rotation and option Michael Wacha to Triple-A instead. Wacha has a 5.40 ERA after his first two major-league starts.