Mastroianni, who is competing for the center-field job along with Aaron Hicks and Joe Benson, said he originally injured his hamstring in early December while playing in the Venezuelan Winter League. But he said the injury is only minor and that he was taken out for precautionary reasons.
"It's fine," said Mastroianni, who was 2-for-3 with a run scored in Thursday's 7-1 victory. "It's just something we've been working on down here. It's been lingering since I was in Venezuela. It's something that doesn't bother me when I'm running. It's only when I'm decelerating. It should be gone in a couple days, so I'm not worried about it."
Rhett Bollinger is a reporter for MLB.com. Read his blog, Bollinger Beat, and follow him on Twitter @RhettBollinger. This story was not subject to the approval of Major League Baseball or its clubs.