ARLINGTON -- Six months ago, the A's lent Ben Sheets a large dose of confidence by offering him a one-year deal worth $10 million plus incentives.

In return, Sheets accepted, acknowledging his own form of confidence in a youthful A's team, one he knew was taking a pretty steep chance with him and his surgically repaired right elbow.

At the time, Oakland was forced to envision both a best-case scenario -- a healthy Sheets guides the A's to the playoffs -- along with a worst-case scenario for cautionary measures, that being another injury-plagued year.

On Wednesday, the latter was confirmed when manager Bob Geren announced that Sheets, who consulted with orthopedist Keith Meister on Tuesday and Wednesday, will miss the remainder of the season with a torn flexor tendon in his right elbow.

According to the A's skipper, a second elbow surgery -- the first caused him to miss all of 2009 -- has not been scheduled, and there was no indication that one will be in the near future. Sheets, 31, will be a free agent at the end of the year, so he could potentially choose to elect retirement rather than face another procedure and the process of finding a team.

Nothing of the sorts has been determined, though. After all, the news was just settling in with Geren, who has already watched Justin Duchscherer and Ryan Sweeney go down to season-ending surgeries

"He'll be missed both on the field and off the field," he said. "He's been a great teammate for a lot of the young guys. A lot of them looked up to him for his competitiveness and, off the field, he was just a pleasant guy to be around."

Sheets, who posted at least six innings in each of his last 14 starts, was initially placed on the 15-day disabled list on Saturday following a pair of outings that brought about inflammation in his troubled elbow.

Surprisingly, the A's pitcher put together rather impressive numbers during those starts, which resulted in just a combined two runs. But those numbers, no matter how they read in a box score, didn't say as much as the one that read on the radar gun, Sheets insisted at the time.

"I was still successful with the diminished velocity," he said. "It didn't fool me, but I was still able to pitch. When I knew my stuff wasn't there, I knew it wasn't going away. ... Swelling's no good. I know that. Your arm just doesn't swell. Things just don't swell for no reason."

Sheets also expressed that at no point this season did he feel a strong progression toward his old self, the one that was a four-time National League All-Star while with Milwaukee. He was 4-9 with a 4.53 ERA in 20 starts for the A's and has allowed an American League-leading 57 extra-base hits.

"The whole year's been frustrating," he said. "From where I was before spring, it's never really taken any jumps you always hear about. To say I felt good for extended periods of time would be false. I felt good here and there -- a couple innings here, a couple innings there, but nothing sustained throughout the year."

With lefty Brett Anderson's impending return to the mound Friday in Chicago, the A's still boast five healthy starters, the other four being Trevor Cahill, Dallas Braden, Gio Gonzalez and Vin Mazzaro.

"[Sheets] will obviously be missed," Geren said on Wednesday, "but the good news is that Brett Anderson threw a side today and it went well, so he's still scheduled to pitch Friday."

Furthermore, the A's manager has been impressed with Mazzaro's sudden turnaround. The young righty, who began the season at Triple-A Sacramento, has posted six straight quality starts with a 6-2 record and 3.45 ERA in 10 starting assignments this year.

"We have a very young and talented five-man rotation," Geren said. "They've all done a great job, they really have. ... Vin has progressed. Each outing he's gotten better. Straight out of the chute, his strikes have been up and his balls have been down. He's been handling the running game well, he's just doing a lot of things well."