Sheets worked the first three innings before suffering a strained groin at the end of the 3rd.
The issue for Sheets now is whether or not he'll be able to make his next scheduled start.
Sheets missed the last five weeks of 2005 with a torn muscle behind his pitching shoulder, and had off and on problems last season. But he still earned the opening day assignment from Brewers Manager Ned Yost this season and pitched a complete-game two-hitter against the Dodgers in the opener.
Sheets said afterwards that he didn't think it was too serious.