Carlos Carrasco was pulled after four innings Tuesday night with what the Cleveland Indians called left knee discomfort.
Terry Francona said Carrasco was taken for a precautionary MRI.
Carrasco got hurt when he stumbled and fell while covering first base in the fourth inning against the Miami Marlins.
"He kind of bruised it. He fell on it, but he initially felt it in the back," Francona said. "So that's why the medical people felt like let's just rule everything out. Hopefully it's just being precautionary, but we do want to get him checked out."