MINNEAPOLIS — It's not an arm injury.

It's not a back injury.

But it's another injury.

Detroit Tigers right-hander Casey Mize, the No. 1 overall pick in the 2018 draft, has been placed on the injured list Wednesday, retroactive to Monday, with a left hamstring strain. The 27-year-old completed 16 starts in his comeback season from elbow surgery and back surgery before running into a speed bump that will keep him out until after the All-Star break.

"Certainly am happy that it's not anything with my arm or back," Mize said. "It's still not great that this happened, but obviously, it's better than what it could have been."

The Tigers called up right-hander Keider Montero to replace Mize in the starting rotation.

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Mize doesn't have a timeline for his return to the Tigers.

He is expected to miss at least three starts.

"I don't know what the timeline looks like," Mize said. "We got to see how it feels early on, and then make some decisions. I don't know how my body is going to respond. It's really up to getting a good baseline of how we're feeling and make a plan based off that. We're not at that point yet."

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Mize suffered the left hamstring strain on a pitch in the sixth inning of Sunday's start against the Los Angeles Angels, in which he tossed 5⅓ scoreless innings. He initially thought he was dealing with a cramp, but medical tests revealed a strain.

Manager A.J. Hinch was asked about his level of concern.

"We're not going to know until he's not sore and he can move around and get back on a mound," Hinch said. "I don't know how long it's going to be, but it was a definite IL from the time we got him evaluated."

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The timing of Mize's injury derails his positive momentum, having posted a 3.41 ERA with nine walks and 24 strikeouts across 29 innings in six starts in June, including a 10-strikeout performance June 24 against the Philadelphia Phillies. He recaptured the consistent 96 mph fastball velocity he showcased throughout spring training, and he finally unlocked slightly better command of his splitter and slider to help miss some bats.

Before all of that, Mize had a 6.56 ERA across 23⅓ innings in five starts in May.

"I felt like I was doing some good things that I looked to carry over into July, and unfortunately, I won't be able to do that," Mize said. "I wish I could have kept it rolling, but I'm going to have to take a step back, take a breather here and get back at it at some point. I'll come back better and finish strong."

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To replace Mize, the Tigers promoted Montero — not right-hander Matt Manning — from Triple-A Toledo. The 23-year-old has a 9.35 ERA with four walks and 11 strikeouts across 8⅔ innings in two games with the Tigers, as well as a 5.03 ERA with 30 walks and 54 strikeouts across 48⅓ innings with the Mud Hens.

The plan is for Montero to make multiple starts with the Tigers, beginning Wednesday against the Minnesota Twins at Target Field.

"It lined up a little bit better for Keider," Hinch said, "and also given that Casey is going to be out for a bit, it allows for a couple starts in a row, which is something that we've never seen with Montero. He should be in the rotation for a few times."

Contact Evan Petzold at epetzold@freepress.com or follow him @EvanPetzold.

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This article originally appeared on Detroit Free Press: Detroit Tigers' Casey Mize put on injured list with hamstring strain