PHOENIX -- Geoff Jenkins' first question after he finished his five innings of work on Thursday was, "How's Sheeter?"

Brewers right-hander Ben Sheets abruptly exited his second spring start against the A's at Phoenix Municipal Stadium after recording just one out with what a team official called "irritation" of the same back muscle that he tore last August.

The team will know more about Sheets' condition on Saturday, when he visits with head physician Dr. William Raasch. Jenkins is among the Brewers bracing against a serious injury.

"Can't have it," Jenkins said. "We need him."

Sheets tore the latissimus dorsi muscle behind his right shoulder while throwing a curveball on Aug. 26 against the Braves at Miller Park but had been rehabbing successfully this spring. In his previous spring start, against Oakland on March 4, Sheets threw only fastballs and changeups, but on Thursday, he snapped off several curveballs.

Sheets surrendered five Oakland runs on six sharp hits, including Mark Kotsay's two-run home run. He 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 paid a visit to the mound.

Yost signaled immediately for reliever Kane Davis.

"It wasn't a knifing pain," Yost said. "It was a little dull ache back there. So to be safe, we decided that it was enough."

"Ben describes it not as pain, but as an uncomfortable feeling," Brewers assistant general manager Gord Ash said. "[Caplinger] did some manual testing and feels like there is still strength in the shoulder. He doesn't feel like there has been any reoccurrence."

Ash said it is possible that Sheets will undergo an MRI scan, but said, "It's going to be [Raasch's] call. Obviously, he's very familiar with the injury and the progress, having examined [Sheets] numerous times during the winter."

Sheets declined interview requests and slipped out of Phoenix Municipal Stadium before the end of the Brewers-A's game.

The 27-year-old will earn a club-record $11.5 million in 2006, including part of the signing bonus from the contract extension he inked last April. Sheets is scheduled to make a fifth consecutive Opening Day start when the Brewers host the Pirates on April 3 at Miller Park.

"I think there's some concern, but is there major concern? Not really. Not yet," Yost said.

After A's second baseman Mark Ellis led off the game with a stinging single to right field, Kotsay hit the first pitch he saw over the right-field fence for a 2-0 Oakland lead.

After a long fly out by Bobby Crosby, Sheets surrendered three consecutive singles, then an RBI grounder that was misplayed by first baseman Prince Fielder. When Kendall followed with a single that made it 6-0, Maddux decided he had seen enough.

"Put it this way," catcher Chad Moeller said. "[Sheets'] demeanor was not what it normally would be under the circumstances."

Said Yost: "His velocity was good. He threw some breaking balls today, and they were snapping, but he just got out there and started throwing fastballs right down the middle. ... It could have been that he just popped some of that scar tissue, which is a good thing."

Raasch will be in Phoenix this weekend to administer physicals to Brewers' Minor League players.

"I think the good news is that it wasn't pain," Ash said. "I think at this point, it's just premature to speculate. We'll just have to let the doctors look at him."