Oakland manager Bob Geren told the San Francisco Chronicle's Henry Schulman this afternoon that Eric Chavez is headed for back surgery.  The third baseman told the Chronicle's Susan Slusser last month that another procedure "would spell the end to his career."The 31-year-old third baseman has a career batting line of .268/.345/.482 over 11 major league seasons, but has appeared in just 121 games since the start of the '07 season.