Zorn: Redskins will be cautious with Portis

Running back Clinton Portis was knocked out of Sunday's 31-17 loss to the Atlanta Falcons in the second quarter, suffering an apparent concussion on a run that was later called back because of a holding call. Portis, the Redskins' leading rusher on the season, took the ball from quarterback Jason Campbell and ran over left tackle with three minutes, 26 seconds left in the first quarter and the Redskins trailing 7-0. Center Casey Rabach held on the play, but Portis fell hard to the Georgia Dome turf when he was tackled by Atlanta defensive backs Chevis Jackson and Thomas DeCoud. Portis lay face-down on the turf for a few seconds before team athletic trainers rolled him over. Coach Jim Zorn said Portis was "knocked out." "You tell me what happened," Portis said after the game. "I don't remember what happened."