By Ian Browne / MLB.com BRADENTON, Fla. -- Andrew Miller's spring has been one of great annoyance. The lefty feels more comfortable throwing the ball than he has in a long time. Yet injuries continue to impede his progress.Miller limped off the mound with a mild left hamstring strain on Tuesday night, and it's unclear when he will be able to pitch again."He limped into the food room [this morning]," Red Sox manager Bobby Valentine said. "That's all I saw. That's new, and not good. Left hamstring strain. He reported this morning with soreness and stiffness. It will be a little [more] clear in 24 to 48 hours."We needed a lefty out of the bullpen anyway but I would like for this kid to get healthy so he can get some confidence.