"We think he's going to help us more there right now," Astros manager Cecil Cooper said. "A little bit of inconsistency the last month or so. We think we have some other options to try."
Right-hander Runelvys Hernandez, currently with Triple-A Round Rock, could replace Chacon in the rotation.
Chacon is no stranger to shifting roles. Out of his 269 career appearances, 134 have been starts and 135 have been in relief.