KANSAS CITY -- The Cardinals' medical team diagnosed left-hander John Gast with a left lat strain Monday, a day after the club placed him on the 15-day disabled list.
"The timetable is to be determined, but the good news is that it's not the shoulder or the elbow," general manager John Mozeliak said. "Hopefully, it's something that won't take too long. With a lat, it can be up to a month or a month and a half. We'll see."
Gast was 2-0 with 5.11 ERA over three starts before the injury, throwing 12 1/3 innings.
Mozeliak was also encouraged that right-hander Jake Westbrook threw Monday with no ill effects. Westbrook has been battling right elbow discomfort.
"Clearly, the news of him throwing [Monday] was far more encouraging than it was three or four days ago," Mozeliak said. "I think there's a lot of positive there. He feels good about where he's going. Directionally speaking, seeing him maybe out on a rehab [assignment] in a week or two would be great."
Mozeliak wants to temper expectations on Wacha
KANSAS CITY -- With right-hander Michael Wacha set to make his Major League debut in a Thursday start against the Royals, the Cardinals settled a short-term dilemma. But whether the highly touted Wacha will be a long-term fixture in the St. Louis rotation this season is still to be determined, according to general manager John Mozeliak.
"There are a lot of questions on what this will look like in terms of usage," Mozeliak said. "Will he be here for the entire season? These are questions we don't have answers to at this time. We are going to be very cognizant of pitch counts and innings, because [Wacha] was pitching at Texas A&M a year ago."
Due to a rash of pitching injuries, the Cardinals had a void in their rotation and decided their fourth-ranked prospect, according to MLB.com., was the best option for Thursday. Wacha, 21, was the 19th overall pick in the 2012 First-Year Player Draft and turned some heads with a superb Spring Training. He followed that with a 4-0 start at Triple-A Memphis and posted a 2.05 ERA in 52 innings. Wacha was scratched from a scheduled start Monday at Memphis, as the Cardinals considered their options.
Mozeliak met with the Cardinal staff Monday night, and much of the discussion was about ways to protect Wacha.
"The key, from my perspective, is that we just have to manage expectations a little bit," Mozeliak said. "He's a year removed from college and being thrust into a very competitive division with a lot of expectations being put on him. I don't know how fair that's going to be. I just think people need to be patient.
"In an ideal world, we wouldn't have to go down this path. But due to all the injuries, we do need some help. He has certainly been our best starting pitcher at Triple-A."
The Cardinals will have to make a corresponding move on their 25-man roster when Wacha is activated for Thursday's start.
Mozeliak understands the hype about Wacha after the right-hander threw 11 2/3 scoreless spring innings, allowing one unearned run on seven hits with one walk and 15 strikeouts.
"It's well-deserved," Mozeliak said. "He was really good this spring and he hasn't disappointed at Triple-A. We're just going to take it day by day. He's a talented young man and he may be here for awhile."
Matheny gives Molina, Kozma night off in KC
KANSAS CITY -- Catcher Yadier Molina and shortstop Pete Kozma have been playing regularly and hard for the Cardinals, and manager Mike Matheny decided Tuesday was the right time to give both players a night off.
Tony Cruz was in the lineup at catcher, and Daniel Descalso played shortstop, with Matt Carpenter slotting in at second base. Molina started 48 of the first 50 games behind the plate, and Kozma started 47 at shortstop.
Molina's rest came one day after a season-high four RBI performance in Monday's 6-3 win against the Royals.
"[Molina] won't shut it down all together because he knows anything can happen," Matheny said.
The Cardinals don't have another off-day until June 10.
Robert Falkoff is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.