updated 3:10 p.m. ET Sept. 18, 2008

CHICAGO - The Milwaukee Brewers were counting on Ben Sheets to make two more starts over the final 10 games as they try to overcome a September slide and reach the playoffs.

Now they're unsure if their All-Star right-hander will be available at all. Sheets left his start against the Cubs on Wednesday night after two innings with a sore right elbow.

"Don't know yet," assistant general manager Gord Ash said Thursday. "He'll get his treatment. We just have to literally play it day-by-day to see when he might be available."

Ash said the issue now is how much the elbow hurts. Sheets' next scheduled start is Tuesday against the Pirates at Miller Park. He was also expected to pitch the season finale Sept. 28 against the Cubs in Milwaukee.

"It's not serious to the point where it's career-jeopardizing," Ash said. "There are no structural issues. He's got pain. Sometimes he can pitch with it, sometimes he can't. Last night was one of those that he couldn't."

Interim manager Dale Sveum, whose team was one-half game out of the wild card entering Thursday's game, said losing Sheets "would be a big blow."

"We'd have to make all kinds of adjustments again," he said. "Until we find out more in the next couple of days, nothing else to say."

The 30-year-old Sheets, who has a 13-8 record and 2.98 ERA this season, is expected to command plenty of attention in the free agent market after the season, despite his history of injuries.

He averaged only 21 starts a year from 2005-07 when he was on the disabled list five times. This season he's also been bothered by groin and triceps injuries but has made 30 starts.

Now, the elbow.

"It's been so up and down that I would think it's very possible," Sheets said Wednesday night when asked if he would pitch again this season. "There's been really good days and really bad days. There's been days where it's hard to move it and it's stiff. Then the next day it's great. So we'll see."

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Sheets said he began to feel some discomfort in the bottom of the first Wednesday night when he faced Derrek Lee, the Cubs' No. 3 hitter. But he told reporters after Milwaukee's 6-2 win that his elbow had been bothering him since an Aug. 26 appearance against the Cardinals.

He said earlier he had an MRI that showed no structural damage and also received an in injection. The elbow had been responding to treatment, he said, but he felt a tug in the first inning Wednesday night.

"He went from 93 mph to 86-88," Sveum said.

After facing Lee in the top of the first, Sheets came to bat and it was apparent his arm was hurting by the swing he took

"He couldn't keep his top hand on the bat. So that was kind of a red flag," Sveum said.

Sveum said he was not aware of Sheets' earlier injection for pain.

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"All I knew was he threw good in the pen, he felt good and he threw good on the side the other day. So everything was fine until that at bat, he said, against Derrek Lee. He came out throwing 93 and obviously something happened," Sveum said.

Sheets wasn't available for comment Thursday.

Ash said the Brewers would not rush Sheets back and they've also been patient with Yovani Gallardo, who has been on the DL since May 2 with a torn ligament in his right knee.

"These guys have futures. It's not our job to just win ballgames," Ash said.

If Sheets is unable to go, Sveum said one option is to go with a four-man rotation or to return lefty Manny Parra to a starter's role. He'd been sent to the bullpen earlier this week and replaced by Seth McClung. The rotation also includes CC Sabathia, Dave Bush and Jeff Suppan.

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