Youkilis fouled a ball off his left shin in the top of the first inning on Thursday night and exited the game in the bottom of the second.
"He's sore," said Red Sox manager Terry Francona after Boston's 4-2 victory over the Angels in 11 innings. "He was X-rayed and they were negative, which is good. He'll be re-evaluated tomorrow. He's pretty sore."
After sustaining the injury, Youkilis finished that at-bat, grounding into a 6-3 double play.
Jed Lowrie moved from shortstop to third base, and Marco Scutaro entered the game at short and took over the cleanup spot for Youkilis.