The Cardinals placed Wacha on the 10-day disabled list with a left oblique strain before Thursday night's game against the Milwaukee Brewers. They recalled right-hander John Gant from Triple-A Memphis.
"Everyone has injuries," Cardinals general manager Michael Girsch said. "We've just got to deal with it."
Wacha accompanied the team as it flew to Milwaukee from Philadelphia, but then continued on to St. Louis for the medical scan.
"We have not gotten an MRI yet," Girsch said. "Hope to have it tonight."
Wacha, who leads the team in wins (8-2) and strikeouts (71) in 15 starts with a 3.20 ERA, left Wednesday's start against the Philadelphia Phillies with the injury. He surrendered a two-run homer to Cesar Hernandez in the fourth inning and pitched to one more batter before he was replaced by Mike Mayers. The Cardinals lost 4-3.
It's the third time this season Gant has been recalled. He is 1-2 with a 4.74 ERA in seven appearances, including three starts, for the Cardinals.
Gant could be a candidate for a start Monday against the visiting Cleveland Indians.
"Gant will be available in the bullpen the next few days," Girsch said. "We still feel we have good options in the rotation. They're all capable of going the rest of the way. Obviously, we'd like to get guys back and have more depth."