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09/08/09 8:28 PM ET

Lincecum scratched with back spasms

Giants bring up Bumgarner to replace ailing ace

SAN FRANCISCO -- In a stunning sequence of events, the Giants scratched Tim Lincecum from his start Tuesday night with back spasms and purchased the contract of Madison Bumgarner, the organization's top pitching prospect, who was assigned to face the San Diego Padres instead.

Giants manager Bruce Bochy wasn't certain when Lincecum, a two-time All-Star and the National League's reigning Cy Young Award winner, would rejoin the starting rotation. Bochy did say that Lincecum would return as soon as he's available -- which came as no surprise, given the right-hander's 13-5 record and 2.34 ERA in 28 starts.

"The sooner we can put him out there, the more starts he can get," Bochy said. "... He just needs a couple of days [of rest], 24 to 36 hours, in that area," Bochy said. "Then we'll re-evaluate where we're at with him."

The Giants, who began Tuesday trailing NL Wild Card leader Colorado by two games, face the West-leading Los Angeles Dodgers each of the next two weekends, sandwiched around a three-game series against the Rockies next Monday through Wednesday at AT&T Park.

Bochy said that Lincecum, 25, reported discomfort in his lower left back after the team returned home from Milwaukee on Sunday, underwent a battery of tests and examinations and began taking anti-inflammatory medication. Bochy added that Lincecum felt significantly better Monday, prompting hopes that he could face the Padres. But the Giants didn't want to risk further injury to their valuable hurler.

"We all have occasional back flareups," Bochy said, lumping Lincecum with average human beings. "We're hoping this is all it is and he'll be fine to go here soon."

Assuming Lincecum's ailment indeed developed suddenly, it wouldn't explain his noticeably diminished velocity in recent starts. His fastball topped out at approximately 93-94 mph -- still effective, but a few miles per hour slower than usual.

Lincecum leads the Major Leagues with 233 strikeouts and the National League with 200 1/3 innings. Those statistics are a mixed blessing, because they almost inevitably mean more pitches thrown and greater stress on a pitcher's arm. Lincecum ranked third in the NL with 3,035 pitches thrown entering Tuesday and topped the league in that category with 3,682 last season.

In Lincecum's last start at AT&T Park, Aug. 28 against the Colorado Rockies, the auxiliary scoreboards displaying pitchers' velocity readings remained blank. Lincecum still shut out Colorado on four hits through eight innings.

That was Lincecum's only victory in his previous six starts, though he recorded a respectable 2.89 ERA and struck out 44 while allowing 27 hits in 43 2/3 innings in that span.

Lincecum was replaced by a pitcher whose arrival in the Majors has generated similar anticipation.

Bumgarner, who turned 20 on Aug. 1 and is believed to be the Major Leagues' youngest active player, posted a 12-2 record with a 1.85 ERA at high-Class A San Jose and Double-A Connecticut this season after finishing 15-3 with a 1.46 ERA in 24 starts at low-Class A Augusta last year. He was the Giants' first-round selection in the 2007 First-Year Player Draft -- the 10th player taken overall, like Lincecum in 2006.

Bumgarner pitched five scoreless innings, allowing one hit, in three Spring Training appearances this year. That included three shutout innings against the Dodgers in the Cactus League finale. Bumgarner allowed one hit and struck out four batters in that exhibition, including Manny Ramirez on three pitches.

Bochy said that Bumgarner, whom the Giants had planned to add to their roster after the Minor League season ended Monday, was the Giants' "best option" to replace Lincecum.

"He's had a good year. He's a kid we think a lot of," Bochy said. "Sure, he came up here on the fast track, but he's the best choice we have to put out there. He's the guy who's probably our best starter in the Minor Leagues, just like we brought up [Buster] Posey. He was our best catcher and we needed another catcher."

Bochy said that Bumgarner will add long- and middle-relief depth during the season's remaining weeks, assuming this is his lone start. The Giants needed another left-hander after optioning Alex Hinshaw (12.00 ERA in nine appearances) to the Minors.

To clear room for Bumgarner on the 40-man roster, the Giants designated right-hander Osiris Matos for assignment.

Chris Haft is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.