Kevin Youkilis lined out to shortstop in the bottom of the first inning of Monday nights game with the Indians, and in doing so, injured his right hand. He was seen immediately grimacing as his jogged down the line, and he continued to stretch his thumb when taking the field in the next half inning.
In the top of the third, the Red Sox decided to take him out of the game and avoid further damage (Victor Martinez took over at 1B, with Kevin Cash going to catcher). For now it's being called a "jammed thumb."
Obviously any prolonged absence of Youk would be near disastrous for Boston.