Will Middlebrooks could be headed to the disabled list due to hamstring tightness. He was not in the lineup for Boston against Oakland on Monday night and no timetable has been set for his return. Middlebrooks experienced tightness in his left hamstring after stealing second base in the ninth inning of Sunday's game against the Mariners. "He feels better today than he did yesterday, and better than he expected to be today," manager Bobby Valentine said. "It's not discolored, and that's good, but it's going to be some days."