Youkilis appeared to suffer the injury after lining to short in the bottom of the first. As he ran out of the box, Youkilis flexed his right hand in pain.
He told manager Terry Francona and trainer Mike Reinold he was fine to stay in the game at the start of the second inning. But the discomfort had worsened a bit later, forcing his early exit.
Victor Martinez moved to first base, and backup catcher Kevin Cash was inserted into the game and took over for Youkilis in the No. 3 spot of the order.
Ian Browne is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.