General manager John Mozeliak said Lynn is being held out as a precaution and that he probably could have pitched through the injury, according to MLB.com's Jenifer Langosch.
In 12 starts this season, Lynn has posted a 3.07 ERA with 77 strikeouts and 23 walks. The 28-year-old is in his fifth season with the Cardinals since being selected in the first round of the 2008 draft.
Tyler Lyons will start in Lynn's place on Saturday against the Kansas City Royals after being recalled from Triple-A affiliate Memphis. At 39-21, St. Louis currently sits in first place in the National League Central division.