Porcello could not remember any particular play that brought on the injury. He mentioned the injury to Ausmus in the middle innings, and Ausmus made the decision to pull him as a precaution.
"He fought me on it," Ausmus said. "He wanted to go back out, and he could have in terms of pitch count. But I just thought the safe thing to do would be to get him out of there right now before something bad happens. If he had gone back out there and really injured himself, I would have trouble sleeping."
The Tigers already have one starter working his way back from injury in Anibal Sanchez, who went on the 15-day DL 2 1/2 weeks ago with a ruptured blister on his right middle finger. He felt fine Tuesday after his Monday simulated game, and he's now penciled in as the starter for Sunday night's nationally televised series finale against the Red Sox.
Porcello improved to 6-1 with six innings of one-run ball Monday.
Jason Beck is a reporter for MLB.com. Read Beck's Blog and follow him on Twitter @beckjason. This story was not subject to the approval of Major League Baseball or its clubs.