We all know that the key to the Celtics' success this season is health. Well, it took only three days for the injury big to hit, as Bill Walker will be sidelined 6-8 weeks: (http://www.boston.com/sports/basketball/celtics/articles/2009/10/01/celtics_f_walker_to_have_knee_surgery/?rss_id=Boston.com+--+Boston+Celtics+news) Celtics forward Bill Walker is expected to miss 6-8 weeks after surgery on his right knee. Walker also had surgery on the knee last year.Celtics coach Doc Rivers said Thursday that Walker has a torn meniscus and that he will have an operation on Friday.Walker averaged three points in 29 games last year with the Celtics. He also averaged 18.9 points and 5.3 rebounds in the development league.