PHOENIX -- A's right-hander Justin Duchscherer, a 2008 All-Star and Oakland's projected Opening Day starter when Spring Training opened last month, is headed for surgery on his ailing right elbow and will start the season on the disabled list.

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Duchscherer, who pitched for the first time this spring in a Minor League game Thursday and had to leave after allowing a walk, two singles and a home run, will miss a minimum of six weeks.

A's manager Bob Geren on Friday said the date of the surgery, an exploratory arthroscopic procedure, and the doctor who will perform it, have not yet been determined.

"We can't really answer any questions until we know what they do," Geren said before his team's night game against the visiting Padres.

With Duchscherer, 31, out until mid-May at the earliest, the A's have four spots in their starting rotation available; GM Billy Beane suggested this week that lefty Dallas Braden has a spot secured.

Lefty Dana Eveland, righty Sean Gallagher and top prospects Brett Anderson, a lefty, and Trevor Cahill, a righty, are the frontrunners to fill the remaining spots. Anderson and Cahill, both 21, have not pitched above the Double-A level.

"Any time you lose one of your guys, it's disappointing," Geren said. "It's something we have to overcome as a team."

Oakland's lineup Friday night featured the return to action of third baseman Eric Chavez, who had not yet played defense in a Cactus League game while rehabbing his surgically repaired right shoulder.

With Chavez at third, Orlando Cabrera at shortstop, Mark Ellis at second and Jason Giambi at first, Geren was able to put his projected Opening Night infield on the field together for the first time this spring.

"There's a lot of guys here who would like to pitch with that lineup behind them," said the skipper.

Duchscherer, who will be a free agent at the end of the season, has been on the DL four times in the past three seasons.