[...] baseman Marco Scutaro, a hero of the Giants’ 2012 World Series title run, underwent spinal fusion surgery in Miami, general manager Brian Sabean said Monday, an operation that could end his career. Scutaro, 39, missed all but five games in 2014 with the back injury but continually has said he hopes to return to baseball. [...] this operation makes it unlikely he will return to the Giants before his three-year contract expires after the 2015 season. Sabean said the operation, to fuse the L2 and L3 vertebrae, requires a recovery time of four to six months before any baseball work can begin. [...] after 11 at-bats and only one hit, Scutaro returned to the disabled list and did not return. To clear a 40-man roster spot for Romo, the Giants outrighted first baseman Angel Villalona to the minors. Villalona had been on the 40-man roster since 2011, when the Giants welcomed him back to the farm system after the charge was dropped.