SAN FRANCISCO -- Giants general manager Brian Sabean defended the organization's decision to re-sign second baseman Freddy Sanchez, whose injured left shoulder has rendered him doubtful for the April 5 season opener at Houston.

Sanchez, who received a two-year, $12 million contract extension on Oct. 30, endured left shoulder and left knee injuries and played only 25 games after the Giants acquired him from Pittsburgh on July 29. He had arthroscopic knee surgery on Sept. 30 to repair a torn meniscus.

As for the shoulder, San Francisco's medical staff found nothing alarming when Sanchez underwent a physical examination and an MRI before signing his contract. But Giants head athletic trainer Dave Groeschner relayed that Sanchez reported discomfort in the shoulder once he resumed performing baseball-related activities. Sanchez underwent arthroscopic surgery Dec. 23 in San Francisco to repair a torn labrum and an arthritic AC joint.

Asked if he would handle the Sanchez situation differently if he had the chance, Sabean refused to second-guess himself or anybody else.

"This is something we couldn't pinpoint," Sabean said. "It shows the medical profession isn't perfect. There's nothing more we could have done. We checked out every medical question."

Groeschner said that Sanchez's labrum tear did not show up on the tests the 32-year-old took before signing his contract.

"Sports medicine is not black and white all the time," Groeschner said. "It's hard to see the extent of that. It's not just reading an MRI. There's a lot of interpretation that's involved."

Nothing was known publicly about Sanchez's setback until manager Bruce Bochy mentioned it on a radio show Thursday night on the Giants' flagship station. Asked about the delay in revealing the news, Groeschner indicated that Sanchez and the Giants sought more postoperative evaluation time.

"He knew we couldn't not put this out there, but we wanted to see where he was at," Groeschner said.

Sabean expressed confidence that Sanchez, the 2006 National League batting champion with Pittsburgh, will regain his form in time to contribute this season.

Referring to Groeschner's observation that Sanchez is rehabilitating five to six days per week at the Giants' training facility in Scottsdale, Ariz., Sabean said, "He's on a mission. I don't have any doubt that he'll get back on the field in due order and be the guy that we traded for."

Groeschner said that the Giants won't be able to determine until March whether Sanchez will be ready for Opening Day.

"That's a goal for Freddy," Groeschner said. "I know he's working his butt off right now. It's a possibility but it may not happen, either."

Groeschner added that Sanchez might be able to begin taking ground balls and join conditioning drills after the first week of Spring Training.

Giants pitchers and catchers are due to report to Scottsdale on Feb. 17 and will begin workouts the following day. Reporting day for position players is Feb. 22, with the first full-squad workout set for Feb. 23.

Utility infielder Juan Uribe, who played 38 games at second base last season, will handle the position until Sanchez returns. Mark DeRosa is another option, but Bochy said that he'll remain in left field for now.

Regarding other Giants recovering from injuries, Groeschner said that shortstop Edgar Renteria (right elbow, both shoulders) is "doing very well," throwing three times a week and swinging a bat. Infielder Emmanuel Burriss (left foot) is participating fully in the Giants' ongoing conditioning camp in Arizona.

"He's actually one of our more athletic guys," Groeschner said.