In a battle to win a roster spot, Miller hit a bump in the road, leaving the Red Sox's 9-2 loss with what the club labeled a mild left hamstring strain.
It is the second setback Miller has had this spring. A couple of weeks ago, he was sidelined with left elbow stiffness.
"[He] felt it on the first pitch," manager Bobby Valentine said. "It] would've been better to call [time out at] that time. But I didn't see it on the first pitch. I saw it on the second pitch, as everyone did."
It's too soon to tell how long this injury will set Miller back.
Valentine thinks it's still feasible Miller could break camp as a reliever, but getting stretched out to starting innings might be a bit of a reach due to his latest injury.