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.

Sheets surrendered five runs on six sharp hits --including Mark Kotsay's two-run home run -- and had just given up an RBI single to catcher Jason Kendall when pitching coach Mike Maddux, followed by manager Ned Yost and head athletic trainer Roger Caplinger, visited Sheets on the mound.

Yost signaled immediately for reliever Kane Davis, and Sheets retired to the visitor's clubhouse. The official word from the club was that Sheets "irritated" the muscle, and he will see team physician Dr. William Raasch on Saturday.

"Ben describes it not as pain but as an uncomfortable feeling," assistant general manager Gord Ash said. "At this point I think it's too early to speculate about anything."

Raasch will be in Phoenix this weekend to administer physicals to Brewers Minor League players. Ash said an MRI scan for Sheets is possible.