Wacha went on the disabled list on June 22 with a stress reaction in his right shoulder.
He began a rehab assignment on Sunday and threw just two innings and 34 pitches before the team decided on his return. Cardinals manager Mike Matheny said Wacha might only be allowed to throw around 60 pitches on Thursday.
"The factors that go into it are that he had a good outing last time and he measured up [medically] yesterday and today very strong. And we've made no question about the fact that when he's ready to go, we want him on the mound," Matheny said.
Before going on the DL, Wacha was 5-5 with a 2.79 ERA.
The Cardinals currently sit atop the NL Central by one game over Milwaukee.
- Molly Geary