Wainwright will have surgery later this week, likely Thursday, and recovery time is generally nine to 12 months.
"Unfortunate news, but not unexpected after what we saw," St. Louis general manager John Mozeliak said before the Cardinals played the Philadelphia Phillies.
Phillies first baseman Ryan Howard had a similar injury, sustained on the final out of the 2011 division series against St. Louis. Howard missed the first half of the following season.
"Totally been there," Howard said.
Wainwright was hurt while batting Saturday in Milwaukee. This is the second major injury of Wainwright's career. The right-hander missed the 2011 season while recovering from Tommy John surgery.
He was not at Busch Stadium on Monday. Mozeliak said the pitcher received multiple medical opinions.
Mozeliak said one of two minor league lefties, Tyler Lyons and Tim Cooney, will take Wainwright's turn Thursday. Marco Gonzales and Jaime Garcia are experienced options for the long term and are both coming off injuries.
Gonzales is on the 15-day disabled list at Triple-A Memphis with shoulder tightness and has been cleared to throw on Wednesday. Mozeliak said the 23-year-old Gonzales will have to make at least one minor league start before the team considers recalling him.
Garcia is working his way back from a setback late in spring training and could be ready within a month. Garcia is trying to return from thoracic outlet surgery to relieve nerve compression.
"Our four starters all have to step up," Mozeliak said. "The short-term look is going to have to be internal, and we'll just see how that goes."
The Cardinals entered play Monday with the best ERA from their starters in the majors. Though Wainwright has a 1.44 ERA in 25 innings this season, the Cardinals' other starters have combined to allow 24 earned runs in 80 1/3 innings for a 2.69 ERA, which would rank second in the majors behind the Pirates (2.39).
St. Louis has reached the National League Championship Series in each of the past four seasons and began Monday leading the NL Central at 12-5.
"It's not good news today, but it's not the end of the world either," Mozeliak said. "These guys know they can go out and compete, and they're looking forward to that challenge."
Cardinals outfielder Jason Heyward was out of the starting lineup with what he said was a minor hamstring injury after getting removed from Sunday's game.
"I feel like we're very capable and a very fortunate group to have a pitching staff that can kind of slide in and do their thing," Heyward said. "I think we're still going to have a lot of fun and do a lot of good things."
The Associated Press and ESPN Stats & Information contributed to this report.