breaking news, from sickels' Minor League Ball:

http://www.minorleagueball.com/story/2006/3/9/163938/1926

PHOENIX -- Brewers ace Ben Sheets, who missed the final month of last season with a torn muscle behind his right shoulder, irritated that same muscle and abruptly left Thursday's Spring Training start against Oakland with one out in the first inning.

more if i find it.

Update [2006-3-9 18:9:25 by lboros]: a comment to the same post:

Drew Olson, Brewers' reporter for the Milwaukee Journal Sentinel, just spoke about the injury on the local ESPN affiliate in Milwaukee. He said that Sheets had the worst velocity he's ever seen (and he's covered him his whole career), only reaching the low 80s. He said that it doesn't look good and that if he tore it again, it may be season ending. Drew also thought that this was a sort of unexpected development as Sheets had been coming along nicely and there was no sign of it coming.

http://www.minorleagueball.com/comments/2006/3/9/163938/1926/4#4