Apparently, it was due to more than just a bad day.
"We're a little worried about him. He's got a groin situation going on," manager Jim Leyland told the media prior to Tuesday's game against Toronto.
That groin injury, Fister confirmed, popped up before Sunday's contest even began. He was on the mound throwing his warmup pitches, and on his third throw, the right side of the groin tightened.
"I felt it a little bit early on, and it's just one of those things where you don't really think about it," Fister said. "Just kind of go through whatever you have to go through and pitch. We really didn't think too much about it. It ended up getting tight afterward, and we're addressing it and taking it day by day.
"It doesn't affect pushing off the rubber at all. ... That's why I was able to continue to pitch and be able to get through it."
This is the third injury Fister has had to deal with this season, as he's twice been placed on the disabled list with a strained right rib-cage muscle. He hopes to avoid another stint, but both he and Leyland acknowledged that it's unclear if he'll make Saturday's start vs. the Angels.
"I can't guess that," Fister said. "It's tight today, so we're treating it as we need to, and we're going to kind of play it by ear."
"We're wasting time right now," Leyland said. "Fister has a groin issue. We will have a pitcher, whether it's Fister or someone else for his next start. Period."
Fister said that he will throw at some point during the next few days to get a better assessment of where he stands regarding Saturday. But for now, head athletic trainer Kevin Rand said the plan is for rest and treatment.
"It's just ice and [stimulation] at this point until we get him more comfortable," Rand said. "It's tightened up right now; the soreness isn't any different than what it was. Once we get through that initial part, we'll start working heat and trying to work through it."
Drew Smyly had been scheduled to pitch the second game of a doubleheader for the Mud Hens on Tuesday night but was pulled after one scoreless inning. It's likely the move was precautionary, as he would be the one to replace Fister if needed. Had Smyly thrown longer on Tuesday night, he would have been on four days' rest for Saturday.