Fister's move to the DL is retroactive to Tuesday, the day after he gave up six runs on 11 hits over five innings to the Red Sox on Memorial Day. Though half of those runs came in after a controversial call from the umpires that denied Fister an inning-ending strikeout of Mike Aviles, the point remained that Fister struggled to keep his pitches down and lacked the usual crispness on them.
"It's been bothering him -- after his first start a little bit, then a little bit more, then a little bit more," Leyland said.
Fister said the strain had been sore, but hadn't been a problem for him until Monday's start.
"It was kind of a progressive thing. It wasn't a one-pitch deal," Fister said. "Afterwards, once the adrenaline wore off and everything kind of settled down, we just addressed the situation."
Leyland said that pitching coach Jeff Jones noticed him making adjustments to compensate.
"All I can tell you is that his first start back, his arm angle and everything was right where it's supposed to be, and Jonesy has noticed since then that it's been down a little bit," Leyland said. "I think that's probably [a situation where] he was trying to find a slot where it doesn't bother him. So we're not going to fool with it."
Fister spent Wednesday undergoing tests in Boston, including an MRI exam. The results, Fister said, will be compared to a previous exam once the Tigers return home Friday.
That same day, Casey Crosby will be preparing for his Major League debut against the Yankees as he gets the first shot to replace Fister in the Tigers' rotation. Once Crosby takes the mound Friday night, he'll complete a long, injury-riddled road to the big leagues that saw him overcome two lost seasons to become the high-powered lefty Detroit coveted when it drafted him and signed him away from a football scholarship to Illinois five years ago.
Crosby is 4-2 with 4.26 ERA in nine starts at Triple-A Toledo, with 57 strikeouts over 50 2/3 innings. On Saturday, he fanned 10 Pawtucket Red Sox batters over seven innings of three-run ball.
Crosby was scheduled to start for the Mud Hens on Thursday, while Fister was slated for Saturday. With Crosby now starting Friday, Rick Porcello will slide back a day and pitch Saturday instead.