The San Antonio Spurs have placed Tim Duncan on the injured list with a sprained ankle and say the star forward could miss two-to-four weeks. The two-time MVP is the Spurs leading scorer, rebounder and shot blocker. He was injured in the opening minutes of yesterday's 110-to-101 loss at Detroit. The seven-footer missed two games earlier this month after spraining the same ankle. He entered yesterday's game averaging over 21 points, eleven and a-half rebounds and nearly three blocks in 62 games. To fill Duncan's spot on the roster the spurs have activated sean marks from the injured list.