But the Phils said he "tweaked" his left oblique muscle while throwing in the bullpen earlier in the day, causing him to cut short the session. General manager Ruben Amaro Jr. said they will know more about the severity of the injury after an examination Thursday.
Blanton, who allowed 11 hits and 11 runs in five innings Monday in a Minor League intrasquad game, is scheduled to start an exhibition game Saturday against the Pirates at Citizens Bank Park. He is scheduled to make his regular-season debut April 8 against the Nationals at Nationals Park.
Word about Blanton's setback followed news that closer Brad Lidge received a cortisone injection Tuesday in his right elbow.
If Blanton can't pitch for an extended period of time, right-hander Kyle Kendrick could take his spot in the rotation.
Todd Zolecki is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.