News that center fielder Angel Pagan will have surgery seemed fait accompli. The prognosis is what provided the jolt. Giants manager Bruce Bochy said Monday that after Pagan undergoes an operation Tuesday to repair the hamstring tendon behind his left knee, he will be lost for about 12 weeks, not the six to eight originally expected. That means Pagan will miss almost the entire remainder of the regular season and could be lost for the year if complications arise. Twelve weeks from Tuesday is Sept. 17, when the Giants have 12 games remaining. On the other hand, with a quicker-than-expected recovery, Pagan could be back in 10 weeks after an injury he sustained a month ago is repaired. Either way, the Giants will have to charge into the stretch drive without a key player from their 2012 championship team, who signed a four-year, $40 million contract after the World Series win. "It's a loss. There's no getting around it," Bochy said. "When you lose your leadoff hitter, the guy who led off for you all the way through the World Series and played a significant role helping you win a World Series, there's no question it's a loss." Pagan was expected back in the lineup over the weekend until he reinjured the tendon during a minor-league rehab start. Instead, he will have surgery at the Kerlan-Jobe clinic, performed by Dodgers orthopedist Dr. Neal El Attrache. It is not unusual to have another team's surgeon perform an operation. Bochy said the Giants plan to have Gregor Blanco be the primary center fielder, with Juan Perez in the mix. Bochy has had no conversations with general manager Brian Sabean about promoting Roger Kieschnick, a corner outfielder who has hit well all season at Triple-A Fresno, or Gary Brown, the 2010 first-round pick who struggled for the first two months before going on a hot streak.