DETROIT -- What looked like a cautiously quick hook on Mike Pelfrey after five innings of Sunday's 11-0 Tigers win over the Astros was actually an injury concern. Pelfrey's back tightened up, manager Brad Ausmus said, leading to his exit.
Pelfrey underwent an MRI on his back after the game.
"They're going to take a picture of it, find out what the actual problem is, if it's serious, or not serious," Ausmus said.
Pelfrey's back was an issue before the game, Ausmus said, but he was able to loosen it up enough to make his scheduled start. He retired eight in a row after a double to lead off the game, then stranded the bases loaded in the third inning, but Pelfrey started to feel it again.

"When he came in from the fifth, he mentioned to me his back had tightened up," Ausmus said. "We knew about it before the game. He was able to get loose enough to start the game and pitch five shutout innings, but he was done because of the back at that point."
It's the first time this season the back has been an issue for Pelfrey, who has veered between great outings and subpar ones for the last month and a half after a tough start to the season. He has 21 starts and one relief appearance, the second-most starts on the team behind Justin Verlander, as well as the second-most innings.
If Pelfrey has to miss a turn, the Tigers will have some rotation juggling to do this week. Jordan Zimmermann and Daniel Norris are both hoping to return from the disabled list after Minor League rehab assignments, while Aníbal Sánchez is filling a rotation spot for at least one more turn against the White Sox on Tuesday. The Tigers have been in the market for a back-end starting pitcher, but still appear likely to stand pat at Monday's non-waiver Trade Deadline.