The Dallas Mavericks will begin their season without the cornerstone of their franchise. The team announced today that power forward Dirk Nowitzki has had arthroscopic surgery on his knee, and will not be able to resume on-court activities for six weeks. The surgery was required to treat the same knee ailment that limited Nowitzki somewhat throughout last year. The Mavericks star has missed the last three preseason games in addition to having his knee drained. Team owner Mark Cuban indicated earlier this week that Nowitzki would be fine and might play through the injury, but it now looks like the Mavericks will start their season without the 11-time All-Star.